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Cepaea nemoralis (Gastropoda, Helicidae): The Invited Invader Author(s): Maggie Whitson Source: Journal of the Kentucky Academy of Science, 66(2):82-88. 2005. Published By: Kentucky Academy of Science DOI: http://dx.doi.org/10.3101/1098-7096(2006)66[82:CNGHTI]2.0.CO;2 URL: http://www.bioone.org/doi/full/10.3101/1098-7096%282006%2966%5B82%3ACNGHTI %5D2.0.CO%3B2 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. J. Ky. Acad. Sci. 66(2):82–88. 2005. Cepaea nemoralis (Gastropoda, Helicidae): The Invited Invader Maggie Whitson Department of Biological Sciences, Northern Kentucky University, Highland Heights, Kentucky 41099 ABSTRACT Marauding snails may not immediately come to mind when considering invasive species, but many non- native snails have successfully colonized the U.S. The wood snail, Cepaea nemoralis (L.), is one of the most striking of these introductions, due in part to its attractive shell coloration. This is one of the few snails that people have purposely introduced into their gardens. Several populations are now established in Kentucky, including a newly discovered population in Kenton County. The bright, striped or solid, yellow, pink, and brown shells of this species have long caught the eyes of natural historians and biologists. Populations of these snails are classic model systems for ecological genetics studies. While introduced populations of wood snails seem to have had only minor impact as agricultural pests, they may have the potential to competitively exclude some native species of snails. INTRODUCTION mer (1907) argued in support of recognizing Though snails may not be the speediest of C. hortensis, having observed several mixed beasts, several species have launched success- populations and noting that of the many snails ful invasions of the U.S. (Cowie and Robinson seen paired on tree trunks, he saw no ‘‘mat- 2001; Dundee 1974; Mead 1971). Perhaps the rimonial alliances between these two forms.’’ most glamorous of these invaders is the wood Current taxonomists also take this view, and snail, Cepaea nemoralis (L.). While many gas- the occasional hybrids produced by these spe- tropods rely on stealth and interstate shipping cies are sterile (Jones et al. 1977). Both taxa to fuel their spread, wood snails have another occur in the U.S., and though wood snails are weapon in their arsenals: charm. Their color- known to be introduced, there is disagreement ful shells (see Figure 1) are nearly irresistible on whether C. hortensis is native or was also to small children, nostalgic malacologists, and introduced from Europe (Burch 1962; Dun- many an evolutionary biologist. dee 1974; Jones et al. 1977; Mead 1971). TAXONOMY LIFE HISTORY AND NATIVE RANGE The wood snail belongs to the family Heli- Native to central and western Europe, wood cidae, which includes the bulk of the Euro- snails are widespread in disturbed habitats, pean edible snails. It is a Linnaean species de- from woodlands to fields and yards, but are scribed in 1758 and was originally Helix ne- also found on chalk cliffs and even coastal moralis, until Held established the genus Ce- dunes (Reeve 1863). They are known by a va- paea in 1837 (Abbott 1989). Currently, four riety of common names, the English ones in- species are included in the genus, of which C. cluding banded grove snail, banded wood nemoralis is the type. The specific epithet snail, brown-lipped snail, and girdled snail means ‘of the woods’ or ‘inhabiting woods/ (Abbott 1989; Reed 1964; Step 1901; Turton groves’ (Pilsbry 1939; Reeve 1863; Rimmer 1857). This species has been widely intro- 1907). duced and now has a nearly worldwide distri- Cepaea hortensis, the white-lipped grove bution (Abbott 1989). snail, is considered the sister species of C. ne- Wood snails are obligately outcrossing her- moralis (Jones et al. 1977). Historically, tax- maphrodites, with both individuals exchanging onomists often treated C. hortensis as a variant sperm during mating, and both individuals of C. nemoralis (Step 1901). The two species able to lay eggs afterward (Stine 1989). Like are primarily differentiated by lip color of the other members of the Helicidae, Cepaea snails shells, which seems a minor feature in light of have a bizarre courtship behavior in which the the fact that C. nemoralis is the most variably courting pair stabs each other with sharp, cal- colored species in its genus and perhaps even careous structures, aptly named darts, before among European land snails. However, Rim- mating (Abbott 1989; Pilsbry 1939). Wood 82 Cepaea nemoralis (Gastropoda. Helicidae)—Whitson 83 Figure 1. Shells of Cepaea nemoralis (L.), the wood snail, showing solid pink (left), solid yellow (top), and striped morphs. Note the brown lip characteristic of this species. These European snails have been introduced throughout the northeastern U.S. and occur in at least three counties of Kentucky. snails often mate multiple times prior to egg the aperture of the shell. The dark brown col- laying and can store sperm for up to 15 oration of this lip differentiates C. nemoralis months (Murray 1964). It is not unusual for from the similar C. hortensis. Shell color one clutch of eggs to include offspring from varies from yellow, to pinkish, brown, or oc- two different fathers (Murray 1964). Eggs are casionally even white (Step 1901; Turton buried in moist soil, hatching after about 3 1857). Shells are also generally augmented weeks (Abbott 1989). The snails reach matu- with 1–5 dark brown bands, though unstriped rity in 4 years and may live as long as 5–9 years shells are seen as well (Figure 2). Multiple col- (Abbott 1989; Jones et al. 1977). or variants are commonly found within the Like those of most land snails, wood snail same population. shells are dextral (spiraling to the right), Wood snails, feeding primarily at night, eat though rare sinistral individuals are sometimes a variety of plants, though they often prefer seen (Rimmer 1907; Turton 1857). Mature in- dead plant material to living, and may even dividuals of C. nemoralis reach 2–2.5 cm in forage on dead organisms such as worms or diameter and have five whorls to the shell other snails (Thompson 1996; Turton 1857). (Pilsbry 1939). When the snail reaches full size Among living plant materials, they prefer and ceases to grow, a reflexed lip forms around broad-leaved plants over the tougher grasses 84 Journal of the Kentucky Academy of Science 66(2) their shells on stones to get at the soft snail within. Other birds, including chickens, will sometimes eat wood snails (Howe 1898). Sev- eral snail predators are invertebrate organ- isms, including certain beetles, glowworm lar- vae (related to fireflies), and even predatory snails (Jones et al. 1977; Woodward 1913). Small mammals such as shrews, moles, and hedgehogs also enjoy these slow-moving mor- sels (Dees 1970; Reed 1964; Woodward 1913). SPREAD IN THE U.S. Since the arrival of Europeans, many spe- cies of molluscs have been both purposely and accidentally introduced into the U.S. In recent Figure 2. Typical five-striped wood snail morph. There years, the number one pathway for the intro- is such great variation in shell striping for this species that duction of new land snail species seems to be a coding system has been developed to catalogue it (Howe via infested horticultural materials (Cowie and 1898; Jones et al. 1977). Stripes are numbered from top to bottom. This shell would be coded 12345. A shell with Robinson 2001). Eggs and small individuals only the third stripe present (Figure 3) would be 00300. such as juveniles can be difficult to see when When partial or total fusion of bands is taken into account, intermixed with soil, mulch, or other plant ma- there are hundreds of possible variants. terial (Cowie and Robinson 2001). Many snail species can also self-fertilize or store sperm for up to a year after mating, so one over- which are common in their habitats, and avoid looked adult may be all it takes to pioneer an species with high concentrations of secondary invasion (Cowie and Robinson 2001; Thomp- compounds or physical defenses against her- son 1996). Wood snails specifically have also bivory such as hairs (Grime et al. 1968; been found by the USDA stuck to vehicles Thompson 1996). Oddly enough, they are said and military cargo (Dundee 1974). to particularly favor the leaves of stinging net- The helicid snails, which include C. nemor- tles (Step 1901). They are adaptable in the lab alis, have a somewhat more colorful history of or under cultivation and happily eat lettuce, introduction, as many of these were purposely carrots, fruit, pure cellulose filter paper, and established in new habitats (Dees 1970; Mead even (occasionally) mutton (Grime 1968; Judd 1971). Helicids, such as Helix pomatia, the 1953; Murray 1964; Sowerby 1825; Thompson French escargot, are often prized as choice co- 1996). mestibles. Many helicid introductions can be Though these snails lack operculums which traced back to the kitchen gardens of Euro- would allow them to close their shells, they pean immigrants desiring a renewable source have a relatively high drought tolerance due of snails (Mead 1971).

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