Exotic Snails

Contact: Dick Bean, Maryland Department of Agriculture | dick.bean@maryland.gov

ANNAPOLIS, MD (March 8, 2013) – Exotic and alien species arrive in the US daily. Whether they are brought in intentionally or accidentally makes little difference; the end result can be the same – new introduced pests with potential to cause serious impacts on agriculture, the natural environment, commerce, and human health and well being. Most alien snails (and slugs) are transported inadvertently. Most species are generalist herbivores (plant feeders). Many can act as intermediate hosts of human and livestock parasites. They can potentially negatively affect local agriculture, impact native species, and create a reservoir for further spread of the pathogens they carry. They move silently, on plants, in trucks, airplanes and ships. Their dispersal into new habitats seems to be wholly, or in part, due to human activity, and as such they can be called “travelling” species (Smith, 1989) and “tramp” species (Solem, 1964). Two gastropod tramps and travelers have been found recently in the Port of Baltimore, which is why MISC has chosen them as the March Invader of the Month.

Two species of exotic snails were recently found to be quietly enjoying the ‘Land of Pleasant Living’ in Baltimore. The heads-up on their presence was given by a West Virginia company receiving cargo originating from a maritime terminal in the Port of Baltimore. The terminal owners were promptly contacted and regulatory officials arranged to survey the area. The search target was the snail identified as Eobania vermiculata, the chocolate banded snail. Officials found the species around the holding area, buildings, on trees, and railroad tracks that terminated near the holding area. A second snail species collected during this survey turned out to be a bit more of a concern as it is ”reportable” – i.e. of quarantine signifigance to USDA. Regulators conducted another survey to assess the distribution of this newly uncovered snail – the maritime garden snail, Cernuella cisalpina and found specimens outside of the terminal holding area, along the railroad tracks, and distributed over a much larger area.

Snails are gastropods with external spiral shells that the animals can retract into completely for protection from predators and extreme weather. Eggs are small, globular structures laid in groups, usually white when newly laid, They are often difficult to identify — identification to species level is best left to trained taxonomists. Although we don’t know right now what negative impacts the newly discovered maritime garden snail would have in Baltimore, we do know that a closely related species, Cernuella virgata, sometimes also called the maritime garden snail, has been a serious problem in areas where it was introduced in Australia. The snail frequently climbs to the top of vegetation to escape high temperatures and drought conditions, which wouldn’t be a problem if it didn’t occur in large numbers on cereal crops destined for export. The contaminated crop is unfit for human and livestock consumption, causing huge losses to the farmers. The presence of large numbers of snails in harvested grain elevates the moisture content and promotes secondary infestation by fungal pathogens that produce toxins in the grain. Toxin-contaminated grain is unmarketable, as it is not fit for animal or human consumption. The snail also contaminates pastures.

Imported goods such as tiles, marble and granite slabs from around the world, particularly the Mediterranean region, are known commodities that commonly transport tramps and traveler snails.

In the past 10 years, there have been approximately 12,000 mollusk interceptions at US ports, airports and border crossings. One of the most common routes of entry for snails is on imported tiles. Since 1984, Cernuella spp. and the chocolate banded snail have been intercepted 2,722 times in the US, 55 times in Baltimore ports of entry; in 45 of these shipments were destined for sites in MD.

Cernuella cisalpina is known to be established in coastal Virginia and North Carolina. The chocolate banded snail is not an actionable pest by USDA because it is already too widely distributed in the US. This species is used as food in many countries due to its larger size. Problems associated with these alien snails include quarantine and the associated chemical applications and misery of such status. They can do real harm to nursery stock, grass seed fields, vineyards, tree fruits, small fruits, and grain crops. Worse yet, they can carry diseases and parasites detrimental to native snails and animals as well as people. The rat lung worm, Angiostrongylus cantonensis (Chen), which causes eosinophilic meningitis, a potentially lethal human disease, can be transported by snail mucus on leaves or snail meat.

The challenge now is to see what can be done with the actionable snail, the maritime garden snail. The Baltimore Port terminal took steps to eradicate the chocolate banded snail and results look promising. The maritime garden snail might be controlled or eradicated using one of the commercially available bait products. Relatively environmentally friendly products containing iron phosphate may be recommended choices.

For more information about Invasive Species of Concern in Maryland, visit the Maryland Invasive Species Council.

photos available electronically on request.

Additional information on the Web:
A Snail Tail, Oregon State University