> Habitat & Distribution

Native to South America, invasive pest Pomacea species have spread throughout Florida and into portions of seven other southeastern states at the present writing, as well as to east Asia and through the Pacific islands (Carlsson et al. 2004a, Joshi & Sebastian 2006, Byers et al. 2013).  Invasive Pomacea populations were first reported in Georgia in 2005, appearing in the Alabaha River near Blackshear, and in South Carolina in 2008, at Socastee, near the resort area of Myrtle Beach.  The snail subsequently popped up all around coastal South Carolina, and in 2023 made its first appearance in North Carolina, in the Lumber River at Lumberton.  I have documented the seemingly inexorable spread of Pomacea maculata throughout the southeastern United States in six posts on the FWGNA blog to date, accessible from the links below.

Throughout their introduced range, Pomacea populations are typically found in disturbed environments – retention ponds and drainage ditches with low flow and large standing crops of aquatic macrophytes.  The Lake Marion population seems localized to a small section of lake margin around vacation houses and docks.  FWGNA Incidence rank I-3p, peripheral.

> Ecology & Life History

Pomacea is a voracious consumer of almost any aquatic vegetation (Baker et al. 2010, Burks et al. 2011, Morrison & Hay 2011), including crops such as rice and taro (Estebenet 1995).  They can also demonstrate pedal surface-feeding behavior (Saveanu & Martin 2013).

The snails can survive months of dewatering by burrowing and enclosing their shells tightly (Wada & Matsukura 2011, Yoshida et al. 2014).  Large eggs are laid in pink clusters on emergent vegetation and other solid surfaces above the water line.  Sex determination appears to be oligogenic (Yusa 2004b, 2006, 2007, see also my essay of 11Aug05 below).

Maturity can be reached in as little as three months or may require two years, depending on the environment, with iteroparous reproduction thereafter (Andrews 1964, Albrecht et al. 1999, Martin & Estebenet 2002).  Estebenet & Cazzaniga (1992) estimated r = 0.09 and R = 20.1 for a laboratory population in Argentina.  More recent life history studies have been contributed by Tamburi & Martin (2011) and Yoshida et al (2013).

Pomacea populations can exert significant competition/predation pressure on other populations of freshwater snails (Kwong et al. 2009, Posch et al. 2013), leading to some experimentation with their suitability for the biological control of the pulmonate hosts of schistosomiasis (review by Dillon 2000: 215-219, 300-301).  Pomacea (of all species) are themselves liable to fall prey to the endangered Everglades kite (Cattau et al. 2010), as well as to a variety of other predators (Carlsson et al. 2004b, Xu et al. 2014, Ueshima & Yusa 2015). Overall ecosystem effects of Pomacea invasion have been explored by Fang and colleagues (2010).

Pomacea may serve as intermediate hosts for the rat lungworm, Angiostrongylus cantonensis, although the danger to humans is often much, much overstated.  Underwood et al. (2019) found no evidence of Angiostrongylus parasitism in an extensive sampling program undertaken here in The Palmetto State.  Indeed, the broad survey conducted by Teem et al. (2013) across Louisiana, Texas, Mississippi, and Florida yielded only 8 cases of Angiostrongylus parasitism in 296 Pomacea tested, all from the New Orleans area.

Pomacea was spread through Asia at least partly in a conscious effort by farmers hoping to harvest the snails for food.  Many of the Asian populations are albinistic, with unpigmented bodies and yellow shells, and are often referred to as "golden apple snails" (Yusa 2004a).  Here in the United States most of the populations are pigmented, and their spread seems to have been accidental, perhaps via aquarium hobbyists.  Additional information on the consequences of Pomacea introduction in Texas is available from Howells (2005a & b).  The model of Byers et al. (2013) suggested that the potential range of P. maculata may ultimately extend along the lower coastal plain of the Carolinas as far north as the Virginia line. 

For comprehensive reviews of the biology, ecology, and life history of Pomacea worldwide, see Joshi & Sebastian (2006), Hayes et al. (2012, 2015) and Joshi et al (2017).  For more about the South Carolina populations, see Gooding et al (2018).

> Taxonomy & Systematics

The systematics of the Ampullariidae in general, and of invasive Pomacea in particular, have become quite an active area of research interest in recent years (Cowie & Thiengo 2003, Hayes et al. 2009).  We initially identified the exotic populations introduced here in South Carolina and Georgia as P. canaliculata, although mtDNA data suggested to Rawlings and colleagues (2007) that our populations might better match the nomen P. insularum.  Then a paper published by Hayes and colleagues in late 2012 led us to re-re-identify our local populations as P. maculata, the third name at the top of this page in eight years.  See my essay of 25July13 for more.

Recent data from the Far East suggest that hybridization between P. maculata and P. canaliculata may be widespread, although no-choice mating experiments have returned evidence of reduced hatchability in F1 hybrid egg masses (Matsukura et al. 2013).  Mate choice tests would be a welcome addition to the research program.

> Maps and Supplementary Resources

• Map of Pomacea distribution in the Atlantic drainages (2023)
• A 6.1 cm P. maculata from the SC population at Socastee, with siphon extended.
  
• A photomontage comparing the egg masses of P. paludosa and P. maculata ("insularum").
  

> Essays

• See my post of 11Aug05, "Ampullariids star at Asilomar" for a review of Yoichi Yusa's oligogenic model of sex determination in Ampullariids on 11Aug05, together with some thoughts regarding the ongoing systematic work of Cowie and Hayes.
• I posted the newspaper article reporting the initial discovery of Pomacea in Georgia on 17Sept05.  The essay includes links to a variety of online references and contributions from Bob Howells in Texas.
• See my post of 24May07 for a review of the large book by Joshi & Sebastian, "Global Advances in Ecology and Management of Golden Apple Snails."
• I reported "Pomacea Spreads to South Carolina" on 15May08.  That post also included a couple fresh figures of adults and eggs.
• I updated the South Carolina situation in my "Two Dispatches from the Pomacea Front" on 14Aug08.  That post included links to an SC DNR flier, distribution map, newspaper articles, photos, and more.
• On 25July13 I bundled together several Pomacea News items, including reviews of the papers by Hayes et al (2013) and Byers et al. (2013), as well as updates on the status of our local invasions here in South Carolina, and notes on the toxicity of eggs.
• Although technically restricted, invasive pest Pomacea are not uncommonly offered for sale among hobbyists and in local pet stores.  See my posts of 9Oct 17 What's Out There, 14Feb18 Freshwater Gastropods and Social Media, and 16Mar18 Psst, Buddy! Wanna buy and Apple Snail?.
• I posted another batch of Pomacea news on 13June18, featuring a review of recent research on the specific distinction between P. maculata and P. canaliculata.  See Invasive Species Updates.
• See my post of 6Oct23, Deadly Snails Invading the US!, for news about the first appearance of invasive Pomacea in North Carolina.

> References

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