Deadly Snails Invading the US!

Yesterday evening my wife and I were having supper with family friends when a young lady – very much attuned to social media of diverse sorts, as so many of the youth these days – mentioned that she had been “bombarded” with alerts about dangerous snails in North Carolina.  This was completely out of the blue.  She’s not a biologist – does not follow technical news feeds – just a regular citizen of the Charleston area in her mid-20s.

NCWRC

I, very much the opposite, confessed complete ignorance of the situation.  So, our young friend whipped out her smart phone, deftly touched off three key strokes and a swipe, and there was the news.  Invasive Pomacea of the maculata/canaliculata sort have been reported in the Lumber River at Lumberton, NC.  But my goodness, the hysteria!

The media frenzy seems to have been kicked off by a perfectly responsible press release from the North Carolina Wildlife Resources Commission on Monday 2Oct23 [1].  Initially alerted by a concerned citizen, the NCWRC conducted a survey that did indeed confirm an invasive Pomacea population extending from the I-95 bridge just above Lumberton [2] to a boat ramp about 6 km downstream.  In measured tones, the press release cautioned:

“Apple Snail grazing habits can damage plants used by many native aquatic species and they have even been observed feeding on amphibian eggs. Additionally, Apple Snails can present human health risks. They may carry rat lungworm, which can cause a potentially fatal disease in humans if the snails are eaten raw or undercooked.”

From that relatively innocuous paragraph came the New York Post headline of 4Oct23, “Deadly Apple Snails found along North Carolina River,” and from CBS News, “Invasive snails that can be deadly to humans found in North Carolina.”  But my favourite headline came from the UK Daily Mail, “Invasive Snails Deadly to Humans are Invading the US!” [html] [pdf] 

The Lumber River continues into South Carolina to unite with the PeeDee River about 50 km downstream from Lumberton.  Another 80 km downstream by kayak through impenetrable swamp would bring us to the mouth of the Waccamaw River, from whence it is but 10 – 15 km back upstream to Socastee, SC, where invasive Pomacea were first reported in 2008 [3].  Whether the North Carolina population represents a new introduction, or simply a 150 km expansion of the South Carolina population, remains to be determined.

We saw a similar wave of concern spread through the Myrtle Beach area of South Carolina when the snails first arrived here 15 years ago, although much lower in amplitude and local in extent.  The local newspapers here described apple snails as merely “harmful” or “worrisome,” not “deadly.”

In retrospect, the NCWRC might have added significantly more context to their press release.  South Carolina researchers have found no evidence of Angiostrongylus parasitism in samples of Pomacea taken here in The Palmetto State [4].  Indeed, the extensive 2013 survey conducted by Teem and colleagues across Louisiana, Texas, Mississippi, and Florida yielded only 8 cases of Angiostrongylus parasitism in 296 Pomacea tested, all from the New Orleans area [5].  And as for cases of actual rat lungworm disease in humans, the CDC was only able to confirm 12 cases in the continental USA 2011 - 2017, the majority of which were linked to eating raw vegetables, not snails [6].

So when invasive Pomacea arrive in Virginia, here’s a suggestion for that press release.  Bold the clause, “if the snails are eaten.”  And suggest that the readership resist the temptation to pop one in their mouths.  Everything will be OK.

Notes

[1] Invasive Apple Snails Now Confirmed in North Carolina.  North Carolina Wildlife Resources Commission, 2October23. [html] [pdf]

[2] In my blog post of 13June18, I advocated legislation to build “a big, beautiful wall on the North Carolina line from Cape Hatteras to Tennessee, 50 feet tall by back-of-the-envelope calculation, Pedro himself manning the I-95 guardhouse just two mucus trails and one gigantic traffic jam North of the Border” to intercept just such a Pomacea invasion as North Carolina is now experiencing here in 2023.  See, I told you so.

[3] More about Pomacea in South Carolina:

• Pomacea spreads to South Carolina [15May08]
• Two dispatches from the Pomacea front [14Aug08]
• Pomacea News [25July13]
• Invasive species updates [13June18]

[4] Underwood, E.B., M.J. Walker, T.L. Darden & P.R. Kingsley-Smith (2019) Frequency of occurrence of the rat lungworm parasite in the invasive island apple snail in South Carolina, USA.  Journal of Aquatic Animal Health 31(2): 168 – 172.

[5] Teem, J.L., Y. Qvarnstrom, H.S. Bishop, A.J. DaSilva, J. Carter, J. White-Mclean, and T. Smith (2013)  The occurrence of the rat lungworm, Angiostrongylus cantonensis, in nonindigenous snails in the Gulf of Mexico region of the United States.  Hawaii J. Med. Publ. Health 72: 11 – 14.

[6] Liu EW, Schwartz BS, Hysmith ND, et al. (2018) Rat Lungworm Infection Associated with Central Nervous System Disease — Eight U.S. States, January 2011–January 2017. Morb Mortal Wkly Rep 67:825–828.

The Mystery Snail Color Genetics Project

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  The Mystery Snail Color Genetics Project.  Pp 63 – 74 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

Who among you, my vast and far-flung readership, has not at least once in your life lingered at the face of a hobbyist aquarium to enjoy a “Mystery Snail?”  Show of hands?  One or two of you in the back?

From Ms. Rachel Voss

OK, a bit of introduction may be helpful before we get down to business this month.  The common name “mystery snail” is today almost universally [1] applied to Pomacea diffusa, the most popular gastropod in the home aquarium worldwide, a (relatively) small South American ampullariid domesticated in the late 1960s [3] for the international pet trade.  Such snails were generally identified as Pomacea bridgesii (Reeve 1856) until around 2007, when a team of our colleagues [4] suggested that the nomen diffusa, proposed as a subspecies of P. bridgesii by the German biologist Werner Blume in 1957 [5], might merit recognition at the full species level.

Although small bodied by the standards of the Ampullariidae, and hence not as voracious of aquarium plants, nor as dangerous as pests upon escape into the wild [6], Pomacea diffusa are still large enough to have a personality, which is, in the eyes of many an adoring enthusiast, charming.  Open my essay of [21Dec17] in a new window for more context, and a bit of additional biological background on mystery snails in the home aquarium.

Some not-insubstantial fraction of the popularity of mystery snails derives from their color polymorphism.  Although I have seen at least 15 – 20 named color varieties on the market, consensus seems to suggest eight distinct phenotypes, some with multiple names.  These are depicted in Ms. Brookana Ashley Patton’s colorful figure below, with a standard name suggested for each: gold, jade, ivory, blue, chestnut, brown/black, magenta, and purple.

A simple Mendelian hypothesis suggests itself immediately, does it not?  Three loci, each with two alleles, would yield eight phenotypic categories quite splendidly.  One of those loci must obviously control body color, with albinism (a) recessive under pigmented (A), if the pattern seen almost everywhere [7] throughout the remainder of the animal kingdom is followed in ampullariid snails.

The other two loci seem to control the coloration of the shell: background color (Y) and striping or color banding overtop of it (S).  A peculiarity of this system is that in most other animals, typically, a mutation at the locus assigned to albinism blocks all color production, everywhere.  Three of the eight varieties of mystery snails, however (gold, chestnut, and magenta), demonstrate colorless bodies but colored shells.

The invasive pests Pomacea canaliculata and P. maculata have well-known “golden” variants with a colorless body and plain yellow shell.  The shell and the body phenotypes seem to be inherited together, as a simple Mendelian recessive trait [8].  The “Giant Columbian Rams Horn” Marisa cornuarietis also has a “golden” variant, inherited as a simple Mendelian recessive, but in this case the plain, unstriped yellow shell is born by a snail with a pigmented body [9].

In the mystery snail Pomacea diffusa, the rainbow of phenotypes commonly observed in the aquarium suggests one locus analogous to that seen in P. canaliculata and M. cornuarietis, the dominant wildtype allele (S) encoding dark stripes or bands of pigmentation covering the shell.  The recessive (s) seems to encode no banding or striping, uncovering the yellow or “golden” background shell color.  I am reminded of the banding locus in the European land snail, Cepaea, which became such an important model organism in the early development of population genetics [10].

As for that second shell color locus, variation in background color independent of banding above it or body pigmentation below is unique to Pomacea diffusa, in my experience.  I have never seen anything like it anywhere in The Mollusca.  But two alleles again seem to be involved: let’s suggest a dominant yellow background (Y) and a recessive colorless (y).  The implication of the model is that as many as three separate biochemical pathways seem to control mystery snail coloration, yielding eight phenotypes, such that the wildtype brown/black phenotype is encoded A_Y_S_ and the completely colorless ivory variety aayyss.  If the model holds.

The three-locus model I have outlined above is not new or original with me.  It seems to have been a part of the lore of mystery snail husbandry for many years [11].  And there are most certainly some very clever and resourceful snail breeders somewhere in the world who could confirm it in a heartbeat.  But to this day, no formal test has ever been published.  The entire, lovely system – all those exciting phenotypes and the intellectually-gratifying hypotheses that go with them – remain anecdotal, untested, and undocumented in the world at large.

Because, in all fairness, those clever and resourceful snail breeders who developed all those lovely gold and purple and jade and ivory snail varieties have reaped some not-insignificant financial reward for their time and effort, would like to reap more, and consider the genetics behind their product a trade secret.  I understand that.

But doggone it, I myself am a professional mollusk geneticist, retired and bored, with nothing better to do with my life than science.  I have a testable hypothesis about the inheritance of color polymorphism in a promising freshwater gastropod model, and I want to see it tested.  And if that hypothesis could be confirmed, all those striking genetic markers could be powerful tools to answer all sorts of additional questions about the biology of the Ampullariidae, a fascinating family of God’s critters, like for example, the consequences of multiple insemination, the potential for sperm competition, and the capacity for sperm storage, see five paragraphs further down.

The experiments necessary to confirm our three-locus model for the inheritance of color polymorphism in Pomacea diffusa are not complicated.  But they require time, patience, attention to detail, and some significant experience with a very specialized little corner of animal husbandry.  The ampullariid diet is non-trivial.  The egg laying, the hatching, and the rearing of juveniles all require special techniques.  And the experiment will require space.  Mystery snails are substantial animals – their culture requires relatively large volumes of water.

Kyra's basement, May 2020

I cultured Physa and a variety of other pulmonates in my lab for many years, and a couple prosobranch species as well [12], and was repeatedly surprised, perhaps even dismayed, by the requirement of simple space – just open, flat space on shelf and lab bench.  There were times in my career that I was covering hundreds of square feet culturing snails with a maximum adult size of 30 mg.  Adult mystery snails are two orders of magnitude larger than Physa.  Am I going to go hat in hand and ask my wife for thousands of square feet in our suburban home to culture Pomacea?

So back in 2017, doing research for a six-part series on freshwater gastropods in the home aquarium [14], I started lurking about in [15] Facebook groups formed by mystery snail enthusiasts.  There were at that time 1,818 members of a Facebook group called “Mystery Snail Addiction,” 3,166 members of a group called “Mystery Snails and Aquatic Lovers,” and 5,442 members of a group called “Snails, Snails, Snails.”  And an idea dawned on me.

The idea is called “crowdsourcing.”  Paging through screenfuls of excited chatter about mystery snails, with images and videos about every conceivable aspect of their life habit and zany antics, it occurred to me that I might be able to attract a large number of talented and enthusiastic volunteers for what I decided to call “The Mystery Snail Color Genetics Project.”

So, I whipped up a modest website of eleven pages, including biological background, genetic model, and three pages of experimental design.  In broad outline, I guided potential collaborators through a trihybrid testcross, starting with an ivory line (aayyss) and a brown/black (AAYYSS), backcrossing the F1 to the ivory to test for linkage.  The biggest challenge was that, absent any data on the question, I felt as though we needed to assume that females store sperm for life, and hence virgin females would be required.  Hit the link below in a new window to see the website if you are curious.  Or a pdf of the entire website is available as FWGNA Circular Number 7 from footnote [16] below.

MSCGP

Notice in particular that step #1 for all new recruits to the MSCGP army was to email me.  I really wanted to establish a direct relationship with every volunteer and try to learn a bit about each of them personally.  I didn’t want to discourage anybody, but I did want to make it clear that what we are doing together is real science.  We will have standards.  No screwing around.

I announced the MSCGP to the three Facebook groups on November 8, 2018, appealing for volunteers, pointing interested parties to the website, and inviting email inquiries.  And braced myself at my laptop for the excited torrent of likes, loves, emojis, comments, questions and wisecracks I felt sure would pour forth.

And in fact, my posts on those three FB sites did reap 6 likes and 4 comments.  Zero shares, but I don’t know what a “share” is, in this context, so that doesn’t matter, does it?  How many followers do I have, I wondered?  Am I an influencer yet?

But I will admit to considerable disappointment when just one of those 6 likers and 4 commenters emailed me directly, a nice young man in Australia, who said he would love to become involved, but no ivory mystery snails were available in his country.  And my posts disappeared off the bottom of the feeds of all three of those FB sites in a matter of hours, gone without a trace.

I received a second inquiry in January of 2019, a third in August, and then two more in November of 2019, a year after I posted my appeal for volunteers.  This was not the response that I was expecting, either in quantity or in quality.

All of these inquiries came from folks who had googled up the MSCGP website and were curious to hear any results we might have obtained.  All were keeping mystery snails as pets, and had some success in reproduction, and were intrigued by color variation in the offspring.  No results so far, I always replied cheerily, but would you like to volunteer?  And one of them did.

Ms. Kyra Hall, who was one of the two who emailed me in November of 2019, was the first serious volunteer recruited into the Mystery Snail Color Genetics Project.  She ultimately pushed the effort further than any other collaborator to the present day, hatching out quite a few pure ivory sibships and attempting to rear them in isolation.  She actually got to the point that she needed true breeding wildtype females, to lay clutches of brown/black offspring with which to cross her ivories.  And it was not until this late date, well into the winter of 2019, that it occurred to me that developing a true-breeding dominant line might be more difficult than a true-breeding recessive.

Beach Blvd, Jacksonville.

We have absolutely no idea on the genetic background of the mystery snails we find for retail sale in aquarium stores.  What would make anybody assume that a snail demonstrating the dominant phenotype was true-breeding?  In fact, it might be more fun if they weren’t, so that dominant mothers might lay interestingly diverse and colorful F1 sibships.  The more I thought about it, I could see some argument for the mysterious snail breeders at the Mystery Snail Factory to purposefully outcross their brown/black stocks before retail sale, if for no other reason than to prevent competitors from developing such stocks on their own.

Might a few generations in the wild select out any weirdo genes bred into Pomacea diffusa stocks for commercial purposes?  Might a naturalized population be the best source of AAYYSS broodstock?  Hmmm.  Pomacea diffusa populations are not commonly reported in the wild [17].

I had known the late Bill Frank for many years, primarily as the steward of the quirky and entertaining jaxshells.org website.  Bill discovered a naturalized population of Pomacea diffusa inhabiting drainage ditches by Beach Boulevard in East Jacksonville in 2006, and posted the discovery on jaxshells.org, and it is probably my browsing across his black, blue, and wisteria-hued webpage [html] that brought the phenomenon to my attention.

So, I emailed my buddy Bill, and asked him if he had ever seen any color polymorphism in his Beach Blvd population of P. diffusa.  And he said no.  And so it came to pass that on December 5, 2019, I pulled into the Denny’s parking lot for my rendezvous with Bill.  The man was as colorful as the palate of his webpages.  I cannot remember the last time I met anybody, at any station young or old, so dedicated, so enthusiastic, so enthralled by trash snails in a weedy ditch.  This world needs more Bill Franks [18].

And the English thesaurus needs more choices under the noun, “ditch.”  Here at home in the Carolina Lowcountry, our drainage ditches are dug to carry away stormwater.  They are almost always dry.  But down in Florida, it is my impression that most ditches are mostly wet, and often transmit significant volumes of groundwater.  The water in the ditches that Bill showed me that morning by Beach Blvd was demonstrating some non-negligible flow, even though it had not rained recently, the water clear and coolish [19].

Bill and I were able to find a dozen adult P. diffusa in about two hours’ effort, combing through the ditches on both sides of the road.  Against the background of his long-term observations of the population dynamics, Bill considered this result a very good catch.  I carried our fresh wildstock back to Charleston that evening and sent a subset by overnight express to Kyra the next day.

The females among them were, in fact, very healthy and fecund, and Kyra was able to hatch quite a few nice clutches of 100% wildtype brown/black progeny.  But alas, her efforts to affect an ivory x brown/black cross did not come to fruition.

Kyra had to move into an apartment in late 2020, effectively bringing to a close her budding career in gastropod genetics.  “Life got in the way,” she explained.  But as annus horribilis 2020 unfolded, from worldwide coronavirus panic to nationwide political ignominy, I was somewhat surprised and really quite gratified to receive an additional nine email inquiries from potential volunteers, a broad assortment of hobbyists who had googled for information on the inheritance of color polymorphism in mystery snails and happened upon the MSCGP website.

And again, although most of those nine did not ultimately initiate experiments, as far as I know, several of them did, at least one or two of whom made serious efforts.  And in 2021 I received inquiries from another ten potential volunteers, a subset of whom initiated experiments, a subset of whom made serious efforts.  And in 2022 I received seven additional inquiries.  So that, as 2022 came to a close, I had exchanged at least some correspondence with a total of 31 potential volunteers for the mystery snail color genetics project.  I should at this point acknowledge Joanna Walthuis, Leigh Charest, John Hynes, and Rachel Voss for significant contributions of time and effort to the MSCGP at intervals during our history.

On February 16, 2023 I sent out a group email to the entire list of N=31 in my MSCGP address book, just to see what the current status of our project might be.  I received ten replies, four of which came from volunteers who still have active experiments underway.  The six respondents who have retired from the field were evenly split, three citing technical difficulties and three reporting, like Kyra, that “life got in the way.”

Kyra's Library, February 2020

The bottom line remains, however, blank.  Here about halfway through the fifth year of the Mystery Snail Color Genetics Project, we have yet to record our first datum.  The consensus from the rank and file seems to reinforce a concern I myself have harbored since I first outlined the experimental design back in 2018.  Rearing pairs of snails in cups, even large (20 oz ones) may require an impractical frequency of water change, and scaling up to one-gallon containers may require an impractical amount of space.  I am just not sure that the pretty experiment I have outlined on the chalk board can be conducted in a private residence, by a private citizen with a job other than snail farming.

Would anybody like to prove me wrong, by proving me right?  Shoot me an email at DillonR@fwgna.org.  The MSCGP is still looking for volunteers!

Notes

[1] In yet another demonstration of the folly of legislating common names, the official, AFS-sanctioned common name for Pomacea diffusa/bridgesii is “spike-topped apple snail” [2].  But I suspect that the generic term “apple snail” has become too closely associated with invasive pests for the comfort of the aquarium trade.  For whatever reason, for quite a few years now the breeders and retailers have been marking “mystery snails” on their aquaria of Pomacea diffusa.  And if that’s what it says on your sales receipt, that’s what it is when you get home.

[2] Turgeon, D.D., J.F. Quinn, A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelson, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and G.D. Williams (1998) Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks (second edition), American Fisheries Society Special Publication 26, Bethesda, Maryland, 526 pp.

[3]  I am quoting the “late 1960s” domestication date for P. diffusa from the 1996 book by Perera & Walls, page 36.  Whether all eight color varieties were available at that early date, I do not know.  All varieties were certainly on the market by 1996, as evidenced by their photos in:

• Perera, G. and J.G. Walls (1996) Apple Snails in The Aquarium.  T.F.H. Publications, Neptune City, NJ

[4] Rawlings, T.A., K. A. Hayes, R. H. Cowie, and T. M. Collins (2007)  The identity, distribution, and impacts of non-native apple snails in the continental United States.  BMC Evolutionary Biology 7: 97

[5] Blume, W. (1957) Eine bis heute unbekannte Unterart von Pomacea bridgesii Rve.  Opuscula Zoologica 1: 1 – 2.

[6] We have directed at least ten or twelve posts on the blog to invasive apple snails of the P. canaliculata/maculata type over the last 20 years.  For an entry into their extensive literature, see:

• REVIEW: Global Advances in Apple Snails [24May07]
• Two dispatches from the Pomacea front [14Aug08]
• Pomacea news [25July13]
• Invasive species updates [13June18]

[7] Actually, we have documented two complementing albinism loci in our own favorite experimental animal, Physa acuta.  See:

• Albinism and sex allocation in Physa [2Nov18]

[8] Yusa, Y. (2004) Inheritance of colour polymorphism and the pattern of sperm competition in the apple snail Pomacea canaliculata (Gastropoda: Ampullariidae). Journal of Molluscan Studies 70: 43 – 48.

[9] Dillon, R. T.  (1998-99)  The inheritance of golden, a shell color variant of Marisa cornuarietis. Malacological Review 31/32: 155-157. [PDF]

[10] Cain, A.J., P.M. Sheppard, and J.M.B. King (1968) The genetics of some morphs and varieties of Cepaea nemoralis (L).  Philosophical Transactions of the Royal Society B 253: 383 – 396.  For more, see

• King Arthur’s Lesson [7Sept21]

[11] In 2005 Stijn Ghesquiere added a “Genetics” page to his world-renowned applesnail.net website, without attribution, featuring a three-locus, eight phenotype Mendelian model very clearly developed and demonstrated.

[12] In addition to the Marisa I reared for my 1999 paper [9], I also had one extended experience with Pleurocera proxima [13], which was a huge pain in the ass.  I know, however, that I’m exaggerating about the “thousands of square feet” estimate up above.  But give it to me – I’m trying to avoid an argument with my wife here.

[13] Dillon, R.T. (1986) Inheritance of isozyme phenotype at three loci in the freshwater snail, Goniobasis proxima: Mother-offspring analysis and an artificial introduction. Biochemical Genetics 24: 281-290.  [PDF]

[14] Here’s my entire series on freshwater gastropods in the home aquarium:

• What’s Out There? [9Oct17]
• Loved To Death? [6Nov17]
• Pet Shop Malacology [21Dec17]
• Snails By Mail [24Jan18]
• Freshwater Gastropods and Social Media [14Feb17]
• Psst, Buddy!  Wanna Buy An Apple Snail? [16Mar18]

[15] Here's a funny demonstration of how unlearned I am in the ways of social media.  In my original essay of 6June23 I used the verb "ghosting" here, to describe reading FB posts without commenting or participating in any way.  On 8June23 my MSCGP colleague "Dylan" sent me an email correcting my verb choice to "lurking."

[16] Dillon, R. T., Jr. (2018) Welcome to the mystery snail color genetics project!  FWGNA Circular 7: 1 - 13.  [pdf]

[17] The USGS Nonindigineous aquatic species database lists 42 records of P. bridgesii/diffusa, as compared to 2,948 records for “Pomacea cf. canaliculata/maculata.”

[18] Here is Bill’s obituary: William Michael Frank (18Sep47 – 16Sept22)

[19] In addition to Pomacea diffusa, the "ditches" along Jacksonville's Beach Blvd are inhabited by Pomacea paludosa, Melanoides tuberculata, and Hebetancylus excentricus.

Invasive Species Updates

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  Invasive Species Updates.  Pp 15 – 22 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

Potamopyrgus in Maryland.  Early last September our good buddy Matt Ashton of the Maryland DNR sent me an email with a couple jpegs attached, including the photo below.  Matt was forwarding the report of a concerned citizen with very good reason to think he had discovered New Zealand Mud Snails in the Gunpowder River at the Prettyboy Dam tailwaters, about 30 km north of Baltimore.  See the 21Sept17 article in The Baltimore Sun from note [2] below for more details.

From Matt Ashton, MD-DNR

The Gunpowder is a lovely little river through most of its course, passing through four state parks on its 90 km journey from headwaters in southern Pennsylvania to mouth at the Chesapeake Bay.  In the late 1980s the Prettyboy Dam tailwaters were stocked with brown and rainbow trout, eggs and fingerlings as well as adults, and both populations have now become self-sustaining [3].  Attention from an avid community of fishermen has quite predictably followed.

This is the second population of Potamopyrgus antipodarium reported from a US Atlantic drainage.  My readership will probably remember the first report I posted back in November of 2013, from a small tributary of the Susquehanna River in central Pennsylvania, also heavily fished by trout anglers [4].  Spring Creek is perhaps 50 km north of the Gunpowder headwaters.  The implication would be that the little snails were transported from Pennsylvania to Maryland via muddy waders or bait buckets.

From the mouth of the Gunpowder to the heart of our nation’s capital is but another 80 km.  I understand that legislation has been introduced in Congress to build a big, beautiful six-inch wall from the Delaware River to the West Virginia line, with a three-inch guardhouse on the Baltimore/Washington parkway.

And (less surprisingly) in Syracuse.  The Great Lakes populations of Potamopyrgus are much older than the Atlantic populations; New Zealand mud snails were first reported from Lake Ontario as early as 1991 and Lake Erie in 2005.  So, surfing around in the USGS-NAS Nonindigenous Aquatic Species Database [5], I picked up a couple 2016 reports of Potamopyrgus in tributaries of Onondaga Lake, near Syracuse.

The Erie Canal runs from the eastern end of Lake Erie across the width of New York, intersecting Oneida Lake and the tailwaters of several of the Finger Lakes, as well as Onondaga Lake, to meet the Hudson River just north of Albany.  How long will it be until tired, poor Potamopyrgus are tempest-tossed down the Hudson into New York Harbor, to enter Ellis Island through the back door?  Is that one golden, too?

Pomacea progress.  As threatening as an invasion of 5 mm snails down from the north most certainly must be to homeland security, the threat posed by an army of 5 cm snails advancing up from the south is two orders of magnitude worse.  On the plus side, however, we are getting some very good science out of it.

In late 2015 our colleague Ken Hayes and 32 coauthors published a comprehensive review of the biology of the entire family Ampullariidae [6], broader than their systematic paper of 2012 [7] and better-integrated than the big 2006 book edited by Joshi & Sebastian [8].  More than just the economically-important pests and pets, the authors reviewed the entire scientific literature published on all 117 ampullariid species (by their estimate) in all 7 genera worldwide.

But though Ken and his colleagues cast their nets as broadly as possible, what they drew back was almost entirely Pomacea canaliculata.  They concluded with a call for additional research of a comparative nature, including behavioral studies that might reveal patterns that may have played a role in the evolution of the other 116 species.  We most certainly agree.

PhilRice II.  So speaking of Joshi & Sebastian.  Last year the Philippine Rice Institute published a second big collection of research focused on the Pomacea invasion, this volume with our good friend Rob Cowie among the editors [9].  A free pdf download is available from the link below.  

Fig. 7 of Rama Rao et al. [14]

Maculata/canaliculata hybridization.  Since the first appearance of pest Pomacea in North America, I have continued to be especially curious about reproductive isolation between populations of P. canaliculata and what is now called P. maculata.  So perhaps the most interesting Pomacea news in recent years, from my perspective, was the 2008 discovery that P. maculata has been introduced together with P. canaliculata throughout east and southeast Asia [10].

Apparently published a bit too late to be collected in the nets of Hayes and his 32 colleagues was an excellent 2013 study by Matsukura et al. documenting extensive hybridization between P. canaliculata and P. maculata throughout Japan, Korea, Vietnam and The Philippines [11].  Of the 16 populations sampled, 7 (all Japanese) were apparently pure canaliculata.  The remaining 9 were mixtures, including one population that was primarily maculata with a few hybrids, and one that was primarily hybrid, with a few pure maculata and canaliculata.

Even more interestingly, Matsukura performed a set of no-choice mating experiments between canaliculata and maculata, suggesting that F1 hybrid clutches suffer significant reduction in their hatching rates, from around 80% down to maybe 20% [12].

Pomacea release sex pheromones and demonstrate elaborate courtship behaviors, featuring nuptial gifts [13].  It would be tempting to hypothesize that some sort of prezygotic reproductive isolating mechanisms may have evolved in their native ranges, which have now broken down in Asian rice fields, as lions and tigers mate in zoos.  But in a surprise finish, Matsukura and colleagues also obtained a sample of 17 individual Pomacea from 5 sites in Argentina and discovered evidence of hybridization in ten of them!  Even in the home range.  Fascinating.

If maculata and canaliculata cannot tell each other apart, how can we?  Hayes et al. [7] observed that typical egg masses of P. maculata contain significantly more eggs of a significantly smaller size than P. canaliculata, a result that Matsukura and colleagues confirmed in Japan.  But that’s not terribly helpful with an adult in hand. 

So Hayes et al [7] also suggested a variety of distinguishing shell traits [14], including adult size, ratio of spire height to shell length, shell thickness, umbilicus, shouldering, and lip pigmentation.  But just last month Rama Rao and colleagues [15] published an interesting study of 130 Pomacea sampled from 8 populations in peninsular Malaysia, 5 of which turned out to be canaliculata/maculata mixtures, judging from CO1 sequence. 

Rama Rao and colleagues did not employ nuclear markers, and hence could not identify hybrids [16].  But judging from mtDNA haplotype, they selected 26 canaliculata and 26 maculata and performed an extensive series of shell morphological and morphometric analyses, including simple linear measures and ratios as well as the geometric analysis shown in the figure above.  They did discover a statistically-significant difference between the two groups in ratios of shell height to shell width and aperture height, but of such a fine nature as to be practically useless.  The bottom line is that the Pomacea of Malaysia seem to comprise one single heap of big slimy snails, darn near indivisible.

And meanwhile, in South Carolina.  Our colleague Elizabeth Gooding and six coauthors (including yours truly) have just published a statewide survey [17] for Pomacea at the highest latitudes of its current US range [18].  The Socastee/Myrtle Beach area [19] is on the northern tip of USDA cold-hardiness zone 8b, with average annual extreme minimums around 15 to 20 degrees F, or -9 to -6 degrees C.  We report both copulation and egg laying year-round, even in coldest months of winter [20].

I understand that legislation has been introduced in Washington to build a big, beautiful wall on the North Carolina line from Cape Hatteras to Tennessee, 50 feet tall by back-of-the-envelope calculation [21], Pedro himself manning the I-95 guardhouse just two mucus trails and one gigantic traffic jam North of the Border.

Notes

[1] My earlier Pomacea reviews include:

• Pomacea News [25July13]
• Global Advances in Apple Snails [24May07]

[2] Invasive New Zealand mud snails found in Gunpowder River. The Baltimore Sun 21Sept17.

[3] The situation is actually a bit more complicated.  The first 7.2 miles below the dam are managed as a wild trout stream, catch-and release.  Anglers in the next 4.2 miles can keep two trout/day.  And the next 6.1 miles are stocked in the spring and fall with ordinary hatchery-reared trout, creel limit five trout/day.  See MD-DNR-fisheries.

[4] For more about the discovery of New Zealand Mud Snails in central Pennsylvania:

• Potamopyrgus in US Atlantic Drainages [19Nov13]

[5] For my reviews of state and national invasive species online databases, see:

• To Only Know Invasives [16Oct15]
• To Only Know Invasives in My General Vicinity [9Nov15]

[6] Hayes KA, Burks RL, Castro-Vazquez A, Darby PC, Heras H, Martín PR, et al. (2015) Insights from an integrated view of the biology of apple snails (Caenogastropoda: Ampullariidae). Malacologia 58(1–2):245–302.

[7] Hayes KA, Cowie RH, Thiengo SC, Strong EE (2012) Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda). Zool J Linn Soc. 166(4): 723–753.

[8] Joshi RC, Sebastian LS. (2006) Global advances in ecology and management of golden apple snails: Philippine Rice Research Institute (PhilRice), 600 pp.

[9] Joshi, RC, Cowie RH, Sebastian LS. (2017)  Biology and management of invasive apple snails.  Philippine Rice Research Institute (PhilRice) 406 pp.  [PDF]

[10] Hayes, K. A. et al. (2008) Out of South America: multiple origins of non-native apple snails in Asia.  Diversity and Distributions 14: 701-712.

Matsukura, K. et al. (2008) Genetic divergence of the genus Pomacea (Gastropoda: Ampullariidae) distributed in Japan, and a simple molecular method to distinguish between P. canaliculata and P. maculata.  Appl. Entomol. Zool. 43:535-540.

[11] Matsukura, K et al.  (2013) Genetic exchange between two freshwater apple snails, Pomacea canaliculata and Pomacea maculata invading East and Southeast Asia.  Biol. Invasions 15: 2039-2048.

[12] The hatchability experiment was not as neat as one might hope, and the results a bit ambiguous.  See the paper itself [10] for details.

[13] Burela S, Martin PR. 2009.  Sequential pathways in the mating behavior of the apple snail Pomacea canaliculata (Caenogastropoda: Ampullariidae).  Malacologia 51: 157 – 164.

Burela S, Martín PR. 2011. Evolution and functional significance of lengthy copulations in a promiscuous apple snail, Pomacea canaliculata (Caenogastropoda: Ampullariidae).  Journal of Molluscan Studies 77: 54–64.

Takeichi M, Hirai Y, Yusa Y. 2007. A water-born sex pheromone and trail following in the apple snail, Pomacea canaliculata.  Journal of Molluscan Studies 73: 275–278.

[14] There are also anatomical differences between canaliculata and maculata, most notably a difference in penial sheath.  A study of anatomical hybrids would be most salutary.

[15] Rama Rao S, Liew T-S, Yow Y-Y, Ratnayeke S (2018) Cryptic diversity: Two morphologically similar species of invasive apple snail in Peninsular Malaysia. PLoS ONE 13(5): e0196582.

[16] Back in the allozyme days, I could have solved that problem with one afternoon in the laboratory and $30 for reagents.  It does frustrate me that science often seems to lose good old technology in its restless quest for the new.

[17] This is the same survey of which I made passing mention in my essays of November and December of 2015.  Although we did not discover any Pomacea on Hilton Head Island, we do formally report invasive populations of Bellamya, Biomphalaria, Melanoides and Pyrgophorus in our 2018 paper [17].  To refresh your memory:

• The Many Invasions of Hilton Head [16Dec15]

[18] Gooding, E. L., A. E. Fowler, D. Knott, R. T. Dillon, T. Brown, M. R. Kendrick, & P. R. Kingsley-Smith (2018) Life history and phenological characteristics of the invasive island apple snail, Pomacea maculata (Perry, 1810) in stormwater retention ponds in coastal South Carolina, USA.  Journal of Shellfish Research 37: 229 - 238. [PDF]

[19] Yes, the introduction of Pomacea we first reported from the Myrtle Beach area in 2008 may even be spreading.  I understand that the initial site of discovery around that trailer park in Socastee was treated with copper sulfate, but the snails seem to have jumped a couple km SE into ditches and stormwater retention ponds around a sprawl of strip malls and big-box retailers.  For ancient history, see:

• Pomacea spreads to South Carolina [15May08]
• Two dispatches from the Pomacea front [14Aug08] 

[20] Although no juveniles seem to hatch in the South Carolina winter.  One presumes that egg masses laid in the winter will hatch in the spring.

[21] If a 6-inch wall is sufficient to stop a 5 mm gastropod coming south between Baltimore and Washington, then to stop a 5 cm gastropod advancing north from the Carolinas we need 100 x 6 inches = 600 inches = 50 feet.

Psst, Buddy! Wanna buy an Apple Snail?

Editor’s Notes –This is the sixth (and final) installment in my series on the general topic of freshwater snails in the aquarium hobby.  Previous posts have been “What’s Out There?” [9Oct17], “Loved to Death?” [6Nov17], “Pet Shop Malacology,” [21Dec17], “Snails by Mail” [24Jan18], and “Freshwater Gastropods and Social Media” [14Feb18].  It might help you to read (at least) my previous (February) post on this subject before going on to the essay below.

This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  Psst, Buddy!  Wanna Buy an Apple Snail?  Pp 57 – 61 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

First let us clarify the situation as pertaining to law.  In addition to their broader body of regulations regarding the movement of gastropods generally, the Feds have a set of explicit restrictions regarding the importation and movement of ampullariids [1].  Quoting the USDA-APHIS verbatim: 

“aquatic snails in the family Ampullaridae (e.g., Pomacea canaliculata, channeled apple snail), with one exception, may not be imported or moved interstate except for research purposes into an APHIS inspected containment facility. One species complex in the family Ampullaridae, Pomacea bridgesii (diffusa) may move interstate without a permit because these snails are not known to be agricultural pests but are primarily algae feeders. An import permit is required for aquatic snails in order to verify species and examine shipments for contaminants that are agricultural pests.” [2] 

Note that it is not illegal to own, buy, sell, trade, breed or propagate invasive apple snails of the maculata/insularum/canaliculata type, conventionally abbreviated IAS.  Naturalized populations of IAS are already widespread in certain regions of the United States.  I, living in South Carolina for example, could easily gather Pomacea maculata from any number of local retention ponds in my area and enjoy them in my home aquarium.  I cannot, however, ship them to my friends in North Carolina, nor carry them in a cooler up I-95.  Nor can my Tarheel buddies come down here and fetch any.

So in last month’s [14Feb18] essay I shared my impressions from 30 days of monitoring the conversation on a Facebook group called, “Snails, Snails, Snails.”  I tallied eight mentions of IAS during that month, including four separate appeals for purchase, and concluded: “Without a doubt, significant pent-up demand exists within the community of aquarium hobbyists for large, invasive apple snails.”

"Last round of Peruvian Apple Snails"

I didn’t mention it at the time, but I am mentioning it now, because I think it is especially significant.  Among the eight mentions of IAS I logged during my 30 days of observation on Snails, Snails, Snails was one offer to sell.  A pet supply store in South Dakota named “Woofs & Waves” posted the photo above, simply captioned, “Last round of Peruvian Apple Snails for the season.”

This post generated 10 comments, plus about 25 associated replies.  Comments included, (1) Cooooool!! and (2) Oh I wish I could get those, and (3) I want one so bad!  He’d do great in my 110! and (4) what does he charge for those?  Where is he located?

The reply to the previous query was, “$9.99, Sioux Falls.”  Then this discussion followed: “I am sure they wold ship if you asked nicely” and “Pretty sure they can’t cuz those are illegal in many places” and “Yeah, South Dakota is pretty lax on wildlife stuff unless you’re poaching.”

I think that independent aquarium stores may be the primary agents for the introduction and spread of invasive apple snails around the USA.  The survey I posted in December [21Dec17] satisfied me that the big-box pet stores don’t sell them, and the desultory survey of major online retailers I published in January [24Jan18], including Amazon and Ebay, didn’t turn up any.  Are Mom-and-Pop independents, which in the patois of social media are called “LPS” (local pet stores), the well from which North American populations of invasive apple snails spring?

Following this hunch, last week I made a field trip across town to the only independent aquarium store in the Charleston Area, a really handsome shop with great stock and a knowledgeable staff called, “Tideline Aquatics.”  And in addition to the usual assortment of mystery snails and nerites and rabbit snails [4], I found offered for sale a small batch of “jumbo gold mystery snails,” maybe six or eight head in the lot, crammed timidly into the corner of an aquarium on the bottom rack, behind the filter.  These are clearly not our benign little friend Pomacea diffusa/bridgesii.  These are invasive apple snails.  Click for larger:

NOT Pomacea diffusa

And more than just any random IAS, my local pet store is apparently stocking golden-form apple snails, of a kind widely introduced throughout Asia and the Pacific Islands.  We don’t host any golden morphs at all in the populations of Pomacea maculata naturalized here in South Carolina.  I’ll bet dollars-to-donuts that the stock of “Jumbo gold mystery snails” for sale a few miles from my house originated from Asia, probably from dealers not unlike the ones surveyed by Ting Hui Ng and her colleagues in 2016 [5].  See figure #14 in the Ng et al. plate I shared with you all back in October [9Oct17].

And here we also reprise a theme I developed in December [21Dec17] – the mysterious origins of aquarium stocks worldwide which, like any other commodity I suppose, it behooves suppliers to protect.  And the plasticity of the names attached to such stocks.  Common use and legal precedent has developed such that “apple snails” are bad and “mystery snails” are good.  So the “jumbo mystery snail” has been born, to mysteriously arrive at an independent aquarium-stock retailer near you.

And so we have now come full circle, which means that it is time to sum up.  I am charmed, genuinely charmed, by the widespread interest and heartfelt love often demonstrated by aquarium hobbyists toward our mutual friends, the freshwater gastropods.  And I think such interests should be encouraged, if for no other reason than they might blossom.  I cannot see how harvest of wildstock freshwater gastropod populations for the aquarium trade could endanger such populations, at any imaginable harvest rates.  I can see, however, a problem with the spread of invasive species.

Here a tiny and obscure freedom, escaping the notice of our founding fathers, is associated both with a tiny societal benefit, and a tiny hazard.  I can’t think of any solution to the tiny hazard, beyond what we’re already doing.  Let’s just leave that freedom alone, shall we?

Notes

[1] And I should immediately stipulate that some states have their own regulations more restrictive than the Feds.  Our good buddy Joshua Vlach from the Oregon Department of Agriculture informs me that Oregon has a five-page list of invertebrates that are ALLOWED to cross its state lines, and all others are prohibited [3].   The bottom line is the same for IAS, however.  Go home!

[2] US Department of Agriculture, Animal and Plant Health Inspection Service.  Plant Health / Import into the US / Permits / Regulated Organisms and Soil Permits / Snails Slugs.  [html]

[3] This reminds me of a scene from one of the Peanuts videos, where Violet and Lucy tell Charlie Brown, “There were two lists, Charlie Brown.  There was a list to invite, and a list NOT to invite.  And you were on the WRONG LIST!”

[4] The shells of the “Rabbit Snails” were completely encrusted with calcification.  Absolutely unidentifiable.  The ugliest gastropods I have ever seen in captivity.

[5] Ng Ting Hui, Tan SK, Wong WH, Meier R, Chan S-Y, Tan HH, Yeo DCJ (2016) Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLoS ONE 11(8): e0161130.  https://doi.org/10.1371/journal.pone.0161130

Freshwater Gastropods and Social Media

Editor’s Notes –This is the fifth installment of my series on the general topic of freshwater snails in the aquarium hobby.  Previous posts have been “What’s Out There?” [9Oct17], “Loved to Death?” [6Nov17], “Pet Shop Malacology,” [21Dec17] and “Snails by Mail” [24Jan18].  But don’t worry.  Full appreciation of Essay #5 is not contingent upon familiarity with Essays #1 – 4.

This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  Freshwater Gastropods and Social Media.  Pp 51 – 55 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

I am not social, in any medium.  I don’t even text, much less twitter or tweet or insta-chat or whatever it is that the kids are doing these days.  I understand that social media can be effective tools for communicating on a large scale.  I did join Facebook about ten years ago, in order to “like” a political group of which I was serving as an officer [1].  I regretted it at the time, and regret it now.

In any case, about once a week I gather up my courage and log onto Facebook.  And watch in horror as great garbled masses of disconnected conversations and news and opinions and jokes and photos and videos from family and friends and professional colleagues and high school classmates and Sacred Harp Singing Societies are disgorged simultaneously onto my desk in one gigantic, hideous, stupefying dose.

So several months ago, a Facebook friend called my attention to a group called “Snails, Snails, Snails.”  Heart racing with a mixture of curiosity and dread, I clicked over to the homepage for the group, and what to my wondering eyes should appear, but an internet forum for “lovers, keepers, breeders, and sales of freshwater and saltwater snails and slugs,” boasting 5,442 members!

"Gary doesn't smell so good."

It was a closed group.  So I submitted my CV, top five recent publications, and three letters of reference, and was, after some period of deliberation, duly admitted to membership.  And have subsequently been charmed.

What an engaging assortment of odd-lot humanity!  Mostly young, apparently from a wide variety of backgrounds, hailing from all over the world, unified by the love, yes love often and freely confessed, of gastropods.  Most of the members seem to be freshwater aquarium hobbyists.  Posts about marine gastropods are occasional, as are photos of pet land snails, and even peripheral aquarium fauna, like shrimp.  But I would estimate that, of the perhaps 15 – 20 posts per day, at least 80% have to do with somebody’s freshwater aquarium pet.

Fascinated by the social interactions as they unfolded before me, I resolved to log onto Snails, Snails, Snails every day for 30 days, beginning 25Aug17, and monitor all activity.

I recorded 16 different freshwater gastropod categories receiving mention during my month of observation, totaling 375 mentions.  Of that total, 230 mentions (61%) were of Pomacea diffusa/bridgesii, almost universally referred to as “mystery snails,” apparently the most popular gastropod pet in the home aquarium by far.  Indeed, at some point during the month my attention was called to a pair of independently-operating FB groups dedicated exclusively to P. diffusa, “Mystery Snail and Aquatic Lovers” with 3,166 members and “Mystery Snail Addiction” with 1,818 members [2]. 

The discussion seems to focus on husbandry – food, water quality, life history in culture – not too much different from chatter about aquarium fish, I don’t suppose.  One probably reads more of the “How do I tell if Gary is dead” sorts of questions.  One also reads a surprising number of posts sharing “the cute thing I saw Lightning do,” probably very similar to typical social media interactions about cats and dogs.

The next-most-popular category of freshwater snails in social media seems to be the nerites of all species, with 33 mentions on Snails, Snails, Snails for the month.  This is unsurprising, given the results of the survey of big-box pet retailers I reported in December [3].  The remainder of the species with double-digit mentions during my 30 days of monitoring were “Ramshorns” (24), Melanoides tuberculata (19), Physa (17), Assassin snails (14), and “Rabbit Snails” (Tylomelania, all species) with 10 mentions [4].

I tallied eight mentions of “apple snails” during my month of observation, by which I was able to unambiguously confirm that the author was referring to large, invasive Pomacea maculata/insularum/canaliculata types.  I also caught two mentions of the invasive “Columbian Rams Horn” Marisa.

One young lady in Houston shared an article from the Houston Chronicle entitled, “Harvey Floodwaters bring weird pink things to the Houston landscape [5].”  There were 11 comments and replies, most of the “LOL” sort.  But other comments included "I'll take them 😄" and "I wish I could find some of these here," and "So jealous!  I'm in Illinois and haven't been able to get my hands on a pair."

Without a doubt, significant pent-up demand exists within the community of aquarium hobbyists for large, invasive apple snails.  I counted four separate appeals to purchase such animals during my 30 days of observation, generally of the form, “Does anyone have a LARGE (like, baseball sized) apple snail that they would sell? I LOVE snails and I can't find any that large near me.” 

It is impossible to know, of course, to what extent such requests are satisfied through one-on-one “messaging.”  Typical public replies to such solicitations included “You’d have to find locally. So you should post your location. Shipping adults is dangerous.” or “For channeleds you'd have to find a local seller. I believe it's illegal to ship them over state lines.”  Here’s one (especially revealing) reply: “Haha thank you! Yes our aquarium shop gets lucky once in a great moon and they have a personal tank with one literally apple size so I am always checking in.”

I never saw any misgivings expressed by any member of the Snails, Snails, Snails FB Group about the potential for large apple snails to become invasive pests.  Significant qualms were not uncommonly expressed, however, about the potential for large apple snails to destroy valuable aquarium plants.  One member asked, “How do you stop apple snails from eating your expensive plants?”  After several commiserations, condolences, and expressions of despair, the Group Administrator posted this meme, which I do not understand:

Finally.  I leave you on this Valentine’s Day with one woman’s heart-wrenching testimonial to the love she bore for her gastropod friends.  She posted: 

“My son was in a horrific car accident on Tuesday and almost lost his life. He is home now and doing well but, while i was away i had my kids feeding my snails for me. It did not turn out so well. I lost a banjo catfish, a betta, and all but two of my big apple snails. I am praying these two guys will recover but idk.”

Yes, you read that correctly.  Her son was in an automobile accident, and she is praying for her snails.

Notes

[1] The South Carolinians for Science Education. [SCSE]  Like us on Facebook!

[2]  The list goes on and on, actually.  A simple search for “snails” within Facebook will also return groups called “Land Snails” (742 members), “Tree and Land Snails” (925 members), “Snail Enthusiasts: USA” (1,400 members) and even (I wish I was kidding) “Giant African Land Snails” with 5,800 members.

[3] Pet Shop Malacology [21Dec17]

[4] Others mentioned included Bellayma (6), “Pagoda snails” (5), Thiara scabra (3), “Devil’s Spike” (1), Lymnaea peregra (1), Gyraulus parvus (1), and New Zealand Mud Snails (1).

[5] Houston Chronicle (7Sept17).  Harvey Floodwaters bring weird pink things to the Houston landscape. [html]

Snails by Mail

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2023c)  Snails by Mail.  Pp 45 – 49 in The Freshwater Gastropods of North America Volume 7, Collected in Turn One, and Other Essays.  FWGNA Project, Charleston, SC.

Last month we surveyed the elements of the freshwater gastropod fauna widely available to hobbyists in the Big Box retail outlets that seem so dominant on the landscape of aquarium supply today [1].  We found two categories of snails reliably offered for sale, strikingly different in their biology but ironically similar in their provenance – the “mystery snails” (Pomacea bridgesii/diffusa) and the nerites.  But, as my readership has already doubtless inferred from my essay of 9Oct17 [2], ampullariids and neritids do not the entire market comprise.  What else might be available online?

Assassin Snail - Aquatic Arts

If one simply enters “freshwater snails” on the subject line of a google search, the first 50 hits include four major retail suppliers – Amazon, eBay, aquaticarts.com, and liveaquaria.com.  Most of the stock available for purchase from these sources are (once again) nerites or mystery snails in their various color varieties.  But below I have compiled a brief review of the remainder, sorted into seven pigeonholes.  The first four taxa or groups of taxa appear to be widely available for purchase online, the next two categories seem to be occasionally available, and the last category is what I would call a “wastebasket.”

Ramshorns – These easy-to-culture snails seem to have remained a perennial favorite of aquarium hobbyists for many years, at least since I was a kid.  All the stocks with which I had any personal experience growing up were North American Helisoma trivolvis, but today it is my impression that most "ramshorns" are Floridian Helisoma scalaris duryi [3].  Ng and colleagues [4] identified Singapore ramshorns as Oriental Indoplanorbis exustus, on the other hand, and I've even seen European Planorbarius corneus implicated in what seems to be a global planorbid conspiracy.  What the heck are these snails?  Most of the offerings for sale online today are “red ramshorns,” which are actually albinos, their absence of body pigmentation allowing that red hemoglobin so characteristic of planorbids to show through.  Stocks with wild pigmentation are marketed as either “brown” or “black.”  There is also a “leopard” variant for sale that has patchy pigmentation on its mantle, and a “blue” that (I think) demonstrates some sort of mutation in shell pigmentation.  I wish I knew more about that, too.

Assassin Snails – Approximately thirty nominal species of the nassariid genus Clea (or Anentome) burrow in the soft bottoms of broad, coastal rivers from southern China and Southeast Asia into The Philippines.  What fascinating creatures!  The group is one of only two neogastropod genera to have successfully invaded fresh waters [5].  As their name implies, assassin snails are predatory – hunting other freshwater snails and sucking them out of their shells.  The little tigers widely marketed to the aquarium hobby today are universally identified as Clea helena, but the excellent recent study by Ellen Strong and colleagues [6] suggests that commercial stocks may represent as many as four species, none of which seems to match topotypic Anentome helena from Java.

Rabbit Snails – Several species of the pachychilid genus Tylomelania are not uncommonly offered for purchase online, variously marketed as “giant” or “orange” or “golden” rabbit snails.  It may be recalled from my October essay that Ng and colleagues [4] identified four Tylomelania species in the Singapore aquarium trade, all of which are apparently endemic to Lake Pozo on the Indonesian Island of Sulawesi.  Some conservation concern has been expressed, but see the follow-up essay I published on this subject in November [7].

Japanese Trapdoor Snails – Yes, our old familiar Bellamya japonica (or maybe B. chinensis?) often seems to be marketed to the indoor aquarium hobby, generally labelled as "Viviparus malleattus.”  The biology of these large oriental viviparids will be well known to my FWGNA readership, but see my species pages [japonica] and [chinensis] for a refresher.

Rabbit Snail - Aquatic Arts

Pagoda Snails – Several nominal species of the pachychilid genus Brotia bearing heavy, strikingly spiny or tuberculate shells are harvested from the rivers of Thailand and occasionally available from online retailers as “Pagoda snails.”  We touched on these back in October as well.

Chopsticks, Spikes, or Long nosed Snails – Occasionally the discriminating freshwater gastropod connoisseur will find thiarids of the genus Stenomelania offered for sale online.  Again, Ng and colleagues [4] identified four Stenomelania species marketed in the Singapore pet trade, although raising no conservation concerns.  The Discover Life website lists 36 nominal species in the genus, ranging throughout Southeast Asia, Australia, and Oceania.  The most common specific nomina mentioned in the pet trade are Stenomelania torulosa and S. plicaria, both distributed widely from India through Indonesia to China.

The Wastebasket – Although (almost) universally reviled, stocks of the “Malaysian Trumpet Snail” (Melanoides tuberculata) are available for purchase on Amazon and eBay.  This invasive thiarid, apparently native to low latitudes throughout the Old World (in various clones), has been widely introduced into the New.  See my FWGNA species page [tuberculata] for more.  And (if you can believe it) hobbyists with a thirst for the small, brown, and mundane can also purchase Physa acuta stocks from Amazon.  I get the impression that both the Physa and the Melanoides are primarily marketed as prey for Assassin snails.  The Physa listing on Amazon advertises, “great natural food for your puffer.”

What I did not find for sale online last week, thank heaven, was any ampullariid stock other than Pomacea bridgesii/diffusa. I remember in years past being able to purchase, at least occasionally through mail order or mom-and-pop aquarium stores, Pomacea insularum/maculata (“Golden Apple Snails”), Pomacea paludosa (“Florida Apple Snails”) and Marisa cornuarietis (“Giant Ramshorns.”)  But I was unable to find, at least upon superficial search, any listing for any such invasive ampullariids through the major online retail outlets today.

So to conclude.  Should we be concerned that any of the freshwater gastropod groups listed above might escape to become pests here in North America, other than the ones already introduced and spreading?  We have reviewed the criteria for invasiveness on quite a few occasions in the past [7], ultimately settling on two ecological qualities which I have called “weedy” and “different.”  So the ramshorns, trapdoors, and wastebaskets are already here.  And the rabbits, pagodas, and chopsticks are not all that ecologically different from North American pleurocerids, in many cases, nor do their life histories seem especially weedy.  That leaves the Assassin snails.

Could an introduction of Clea succeed here in North America?  Some concern has already been expressed [8].  All the range maps I have seen for the genus seem to suggest that their natural distribution is entirely tropical – apparently ranging from the equator to around 20 degrees N latitude.  So our own Key West floats in the Caribbean at latitude 24.5 degrees N, perhaps still a bit too temperate to raise concerns about the threat of gastropod assassination here in the USA.  But you all down in Mexico and Central America might best be on the lookout.

Notes

[1] Pet Shop Malacology [21Dec17]

[2] What’s Out There?  [9Oct17]

[3] Subsequent to the publication of this essay I posted a lengthy series on Helisoma scalaris duryi, starting in October of 2020 and going onward for at least five or six months.  I do suggest that you skip ahead here and read forward into 2021 if you are genuinely interested in "ramshorns":

• The flat-topped Helisoma of The Everglades [5Oct20]

[4] Ng Ting Hui, Tan SK, Wong WH, Meier R, Chan S-Y, Tan HH, Yeo DCJ (2016) Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLoS ONE 11(8): e0161130. https://doi.org/10.1371/journal.pone.0161130

[5] The only other neogastropod group to invade fresh waters is the marginellid genus Rivomarginella.

[6] Strong EE, Galindo LA, Kantor YI. (2017) Quid est Clea helena? Evidence for a previously unrecognized radiation of assassin snails (Gastropoda: Buccinoidea: Nassariidae) PeerJ 5:e3638 https://doi.org/10.7717/peerj.3638

[7] Loved to Death?  [6Nov17]

[8] For the biology of freshwater gastropod invasions, see:

• Invaders Great and Small [19Sept08]
• Community Consequences of Bellamya Invasion [18Dec09]
• The Most Improbable Invasion [11Oct12]
• The Many Invasions of Hilton Head [16Dec15] 

[9] Mienis HK. 2011. Will the uncontrolled sale of the snail-eating gastropod Anentome helena in aquarium shops in Israel result in another disaster for Israel’s native freshwater mollusc fauna? Ellipsaria 13(3):10-11.  Bogan AE, Hanneman EH. 2013. A carnivorous aquatic gastropod in the pet trade in North America: the next threat to freshwater gastropods. Ellipsaria 15(2):18-19