New Book: Biology and management of invasive apple snails

There is a new, comprehensive book available online:

Joshi R.C., Cowie R.H., & Sebastian L.S. (eds). 2017. Biology and management of invasive apple snails. Philippine Rice Research Institute (PhilRice), Maligaya, Science City of Muñoz, Nueva Ecija 3119. 406 pp.

I am proud to have contributed to the chapter on the “Identity, reproductive potential, distribution, ecology and management of invasive Pomacea maculata in the southern United States” (pp. 293-334)

Check out: Book Cover





Steady Invasion of Florida’s Public Waters by Pomacea maculata

2014 Graph_edited-1

Each year aquatic biologists from Florida Fish and Wildlife Conservation Commission survey all of Florida’s public water bodies – – lakes and rivers with both state sovereignty and public boat ramps. This effort by the Invasive Plant Management Section focuses on aquatic vegetation, especially invasive, exotic plants, such as hydrilla and water hyacinth. In 2006, however, Pomacea maculata was added. Rob Kipker, my former supervisor there, is kind enough each year to provide me with the current data. His chart above shows a steady increase in the number of water bodies invaded by the South American snail. As of 2014, 36% of Florida’s public 450 waters are affected. Even more alarming is that Pomacea maculata can be found in 72% of Florida’s lakes and rivers by area! Jess Van Dyke


The antifeedant and toxic activity of Neudorff’s 3% Iron Phosphate bait on Pomacea maculata


Last November, I was contacted by Lauren Strachan Hall, Research Coordinator for Neudorff North America. Originating in Germany, this company has been a leader in creating natural pesticide products for over 150 years. Ms. Hall coordinates field research for Neudorff, whose guiding principle is to combine a high degree of efficacy with excellent environmental safety.

One of Neudorff’s products, called “Sluggo” (A.I.: 1% iron phosphate), has been effectively used on terrestrial snails in the U.S. and elsewhere, but it is not labeled for aquatic use in the United States. This company has successfully treated invasive, exotic Pomacea canaliculata and P. maculata in Europe and Asia using pelletized iron phosphate baits in water. Ms. Hall expressed an interest in testing a more concentrated product in development (A.I.: 3% iron phosphate), while the company considers E.P.A. registration for its aquatic use in the United States.

Test 2

The protocol called for 8 replicates per treatment with the treatments being 0.5g, 1.0g, 2.0g and 4.0g of NEU1180 HP pellets, plus a “control” of flour-based pellets. The containers were 5.7L plastic containers (30cm X 15cm X10cm). The tops of the containers locked which is important with large Pomacea. Snails were collected from Wellman Pond, east of Tallahassee, Florida. The average weight of the snails was 150g (116g – 178g). Shell height averaged 7.3cm. The protocol called for testing the snails’ appetites at 4DAT, 8DAT, and 12 DAT. Cucumber slices proved to be attractive, long-lasting, and easy to weigh and monitor.


The 3% iron phosphate bait proved to be an attractive to the snails. In fact, the test product appeared more attractive than the flour-based, blank pellets used in the control. The pelletized bait, scattered evenly in the containers, was readily consumed by all snails. The snails were observed daily for “proof-of-life,” e.g. attachment to the side of the container or resistance to a gentle pull on a closed operculum. Deaths were recorded daily. The snails were fed single cucumber slices every 4 days and percent consumption was noted the following day.

In three simple bench tests, Neudorff’s 3% iron phosphate bait appeared to have dose-related, detrimental effects on adult Pomacea maculata in terms of appetite and survival. Supplemental food consumption was reduced by 77% in the 0.5g treatment, 75% in the 1.0g treatment, 100% in the 2.0g treatment, and 100% in the 4.0g treatment. At 12 DAT, survival averaged 92% in the control, 75% in the 0.5g treatment, 50% in the 1.0g treatment, 12.5% in the 2.0g treatment, and 25% in the 4.0g treatment.

Feeding was suppressed at all treatment rates and ceased completely at rates of 2.0g and 4.0g. At those higher rates, 75% of the adult snails were dead by 6DAT. Considering the environmental safety of iron phosphate and the current lack of any safe and effective alternatives, the negative impacts of Neudorff’s 3% iron phosphate bait on food consumption and survival are reasons for optimism for this product’s use to control adult Pomacea maculata. – – Jess Van Dyke

Pomacea insularum is now Pomacea maculata!

P. maculata shells

Dr. Romi Burks from Southwestern University emailed me recently and asked me to “alert people about to the paper by Ken Hayes and his colleagues” that changes the taxonomy of the Island Apple Snail. After Dr. Robert Dillion of the College of Charleston suggested the same thing months ago, I published the abstract of the excellent and exhaustive report Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae in the Recent Reports section of this blog. However, I must admit some defiance (laziness?) to changing the scientific name throughout this site. My poor, old brain just wishes the taxonomists would make up their minds, so I would not have to relearn scientific names. I know I’m not alone. However, as Romi writes, “What’s in a name, one might ask? A whole lot!!” So, it’s official – – Pomacea insularum is no more, or as Ken Hayes et al put it: “Ampullaria gigas Spix, 1827 and Ampullaria insularum d’Orbigny, 1835 are herein synonymized with P. maculata.” Sorry, I’m just the messenger!

Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda) by KENNETH A. HAYES1,*, ROBERT H. COWIE1, SILVANA C. THIENGO2, and ELLEN E. STRONG3, 1Center for Conservation Research and Training, Pacific Biosciences Research Center, University of Hawaii, 3050 Maile Way, Gilmore 408, Honolulu, HI 96822, USA,2Instituto Oswaldo Cruz/Fiocruz, Av. Brasil 4365, 2104-900 Rio de Janeiro, RJ, Brasil,3Smithsonian Institution, National Museum of Natural History, P.O. Box 37012, MRC 163, Washington, DC, WA 20013-7012, USA, Zoological Journal of the Linnean Society, Volume 166, Issue 4, pp 723–753, December 2012;jsessionid=EFB0C1573E4E5BA869B0E679F7F3642F.d04t01?deniedAccessCustomisedMessage=&userIsAuthenticated=false


New USGS Maps Depict Ranges of Exotic Pomacea in the Continential U.S.

Pomacea insularum map 03.19.2013 USGS

USGS Fact Sheet for Pomacea maculata (insularum)


P. canaliculata map 2.15.2013 USGS

USGS Fact Sheet for Pomacea canaliculata

USDA Profile for Pomacea canaliculata


How is the Island Apple Snail spreading so rapidly in Florida?

According to FWC’s data presented at the end of my last post, the Island Apple Snail (Pomacea insularum) was found in less than 1% of Florida’s public waterbodies in 2006. Five years later, its range has exploded to 22% the state’s lakes and rivers. How is that possible for an animal that moves an average of only 14 meters/week (Darby et al., 2002)? None other than Charles Darwin (1859) was also “perplexed much” when contemplating wide distribution of certain freshwater snail species among the distant Pacific Islands.

There are two modes of range expansion for organisms: active and passive. The active mode for mollusks is at a proverbial “snail’s pace.” Nevertheless, snails are common globally, including desert oases and newly formed volcanic islands. Clearly, mollusks possess an extraordinary capacity for passive means of dispersal. In the case of P. insularum, I have witnessed them using temporary buoyancy to move easily with the waves across lakes or with the current of creeks to rapidly float downstream. Such passive mobility can easily explain dispersal within a given watershed. However, I have also seen this primarily-aquatic species quickly and inexplicably appear in newly-constructed, isolated ponds. Passive dispersal by human activities is well-documented and, therefore, usually blamed, but I wonder. Range expansion in such far flung areas just seems too commonplace. There cannot be that many hobbyists recklessly dumping aquaria!

Charles Darwin (1859) conducted an experiment on a theory proposed by Lyell (1832) that external transport by birds is the most likely passive dispersal mechanism of freshwater snails: “I suspended the feet of a duck in an aquarium; where many ova of freshwater shells were hatching; and I found that numbers of the extremely minute and just-hatched shells crawled on their feet, and clung to them so firmly that when taken out of the water, they could not be jarred off, though at a somewhat more advanced age they would voluntarily drop off. These just-hatched mollusks, though aquatic in nature, survived on the duck’s feet, in damp air, from twelve to twenty hours; and in this length of time a duck or heron might fly at least six or seven hundred miles, and if blown across the sea to an oceanic island, or to any distant point, would sure to alight on a pool or rivulet.”

Many researchers after Darwin have been equally “perplexed” by the rapid and/or long distance dispersal of slow-moving mollusks, but a scientific consensus is developing. Vagvolgyi (1975) concluded that small body size facilitated the dispersal of land snails across broad expanses of ocean: “Support to the hypothesis is provided by the facts that land snails have been recovered from the plumage of birds [and] that recently formed volcanic islands have been colonized predominantly by minute land snails.”

In a study of 50 springs widely scattered across the arid regions of Australia, Wilmer et al. (2008) determined that “short range dispersal of aquatic snails occurs via active movement facilitated by aquatic connections among springs while long-range dispersal is likely facilitated by an animal vector (phoresy).” Aubry et al (2006) stated that passive dispersal of an invasive snail in France relied on “a behavior, called the ‘climbing reflex’ – – one of the main and most efficient features in the process of passive dispersal.”

Clearly, the theory that birds transport aquatic snails is not new.  In fact, it is no longer a theory but has been demonstrated convincingly, both experimentally and by field observations. “The pulmonate land snail Balea [has]even managed to travel over thousands of kilometers of open ocean, from Europe to the Azores and the Tristan da Cunha islands, and back again” (Gittenberger et al., 2006). In the case of the Island Apple Snail, I wonder if the “climbing reflex” is innate behavior for newly-hatched juveniles. It would certainly be easy for such small snails to attach to the legs of wading birds frozen in their common fishing stance.

To test that theory, I went back to my favorite experimental site, Wellman Pond, and placed 30 bamboo stakes with diameters similar to those of the legs of wading birds near hatching egg clusters of P. insularum. Upon return, I carefully inspected each stake and found only one juvenile snail. Quoting Gittenberger (2012) again, “Long-distance dispersal implies a series of unlikely events. However, time is available and a single snail may be sufficient for a successful range extension.” In Florida, the distance from lake to lake is relatively short. It seems reasonable to conclude that the rapid range expansion of the Island Apple Snail is via passive dispersal on the legs wading birds. Posted by Jess Van Dyke

Does Pomacea’s Aerial Respiration Requirement Determine Environmental Impact?

Aerial respiration of Pomacea via siphon (Jess Van Dyke)

Though Apple Snails are freshwater inhabitants, they are clearly amphibious. Pomacea possess combed, gill-like structures (ctenidium) for aquatic respiration and lung-like pulmonary sacks for aerial respiration, as well as buoyancy regulation. When dissolved oxygen levels are high (5-6 ppm), the snails remain mostly underwater, but when low (1-2 ppm), they rely on their siphons and “lungs” to breathe fresh air (San Martins et al., 2009). In any case, all Pomacea regularly come to the surface to ventilate their “lungs.” Such behavior is obligatory.  Preventing aerial respiration negatively affects activity, feeding, and survival (Seuffert and Martín, 2009). They must occasionally take a breather!

Darby et al. (2002) reported that Apple Snails prefer to inhabit shallow water areas ( < 50 cm) because of the need to breathe atmospheric air without expending a large amount of energy to move to the surface. Darby (1998) also suggested that unconsolidated organic material may restrict movement into deep water. However, recent observations of healthy Pomacea as deep as 14.6 m (48’) in Apopka Spring indicate that depth alone is not a deterrent to the snails (Bernatis, 2010). Seuffert and Martín (2009) have concluded that Pomacea are unevenly distributed relative to the access to air – – concentrated less than 2–4 m from the nearest emergent substrate. Simply put, Apple Snails need easy access to emergent plants (or other structure), so they can crawl up and catch a breath of fresh air.

According to the annual survey by FWCC, Pomacea insularum is now present in 22% of Florida’s public lakes and rivers (see below). The mystery in Florida is why this invasive, exotic snail will strip one lake and leave the vegetation relatively unaffected in another. Perhaps, three physical features of lakes play important roles: shoreline development, average depth, and mean slope. Shoreline development (SD) is simply the ratio of the length of the shoreline of a lake to the circumference of a circle with the same area as that lake. The higher the SD ratio is the more complex the shape of the lake. Average depth is self-explanatory, and mean slope is the proximity of bathymetric contours to one another. Taken together, these parameters determine the extent of the littoral zone and the abundance of emergent vegetation.

A relatively small, shallow lake with a gradual bathymetry but a complicated shoreline would seem to provide the best habitat for Pomacea insularum. In such a lake, on a per area basis, food would be more abundant; emergent vegetation would always be near for aerial respiration (and egg deposition); and dissolved oxygen would tend to be high, unlike in a deeper lake with an anaerobic hypolimnion. In short, a greater percentage of the lake would be within 2-4 m of substrate that Seuffert and Martín (2009) suggest is Pomacea’s preferred habitat. The greater the density of Pomacea insularum, the more likely the snail population could consume all of the aquatic vegetation in a given lake. Let’s see how this theory plays out. Posted by Jess Van Dyke

Annual Survey of Florida’s Public Waters  for Pomacea insularum by the FWC:


        Area (ac)



















About Snail Busters

The Snail Busters Blog was created to facilitate communication between aquatic resource managers who are fighting the spread of invasive, South American apple snails, specifically Pomacea maculata (formerly P. insularum) and P. canaliculata, in the U.S.

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

Join 35 other followers