Common Name: Rosy Wolfsnail, Cannibal SnailAuthor: Nokmenee Chhun
Scientific Name: Euglandina rosea
Classification:Phylum: MolluscaIdentification: Euglandina rosea is a terrestrial snail with a long and slender body. It can be recognized by its shell, which is pinkish and almost translucent. The shell is usually two to three inches in length, six centimeters in height and two centimeters in width (only Achatina fulica Bowdich is larger). The lips, which are elongated and protrude like tentacles, contain chemical receptors that are used to track prey by following their mucus trails. When it has located its prey, it consumes smaller species whole, while larger ones are manuevered in such a way that their soft parts are exposed for easier extraction. Observation of feeding behavior demonstrates that E. rosea prefers smaller snails, especially if the shell can be swallowed whole, suggesting that a component of feeding behavior is dictated by calcium demands.
Original Distribution: E. rosea is native to the southeastern United States.
Current Distribution: E. rosea is currently found in Hawaii, Kiribai, French Polynesia, American Samoa, New Caledonia, Vanuatu, Solomon Islands, Palau, Guam, Northern Mariana Islands, Papua New Guinea, Japan, Hong Kong, Taiwan, North Borneo, Madagascar, Seychelles, Mauritius, Reunion, India, Andaman Islands, Sri Lanka, the Bahamas and Bermuda.
Site and Date of Introduction: E. rosea was first introduced to the Hawaiian Islands in 1955 by the Hawaii State Department of Agriculture to control the giant African snail (Achatina fulica Bowdich), an exotic agricultural pest that was deliberately introduced for garden decoration in 1936. Since 1955, E. rosea has been introduced to more than 20 oceanic islands as a biological control agent for A. fulica and other snail pest species. Biological control is often used to decrease populations of detrimental species to levels where their impacts are insignificant.
Mode(s) of Introduction: E. rosea has been deliberately introducted to numerous areas to control A. fulica, even though there is no indiction that E. rosea has reduced the populations of A. fulica anywhere.
Reason(s) Why it has Become Established: Human activities often provide a very efficient dispersal pathway for exotic species. E. rosea introduction to Hawaii was deliberate. A species that is deliberately introduced often has a greater chance of becoming established, integrated and subsequently invasive than those that are inadvertently introduced. Deliberately introduced species are often able to establish because a large number of individuals are often released. In addition, these individuals usually receive a great amount of care and attention to promote their growth and reproduction.
E. rosea has become established because it is an r-selected species with generalist food requirements, wide habitat tolerance and efficient dispersal. In addition, the fact that E. rosea is native to the Southeastern United States and was introduced to areas with a similar environment enhanced its chances of becoming established.
E. rosea is a cross-fertilizing hermaphroditic species that lay approximately 25-40 eggs a year. It has a much higher reproductive rate than Hawaii’s endemic land snails, which reach sexual maturity at about five years and have a low reproductive rate, giving birth to an average of only four or five live young a year.
Although E. rosea seems to have a preference for endemic snails, it is certainly not a food specialist. It will not hesitate to consume other wolfsnails. Upon hatching, young wolfsnails immediately look for prey and smaller siblings are often eaten. The wolfsnail further supplements its diet with the numerous slug species found in Hawaii as well as the other non-indigenous snails that were introduced for control of A. fulica.
E. rosea is a habitat generalist and lives in both disturbed and undisturbed areas. It has expanded its range from disturbed areas infested with A. fulica and spread into the native forests, into higher elevations where Hawaiian endemic tree snails are found. Although considered a terrestrial invertebrate, in its native habitat, it has been seen crawling up trees and has been known to go underwater in search of its prey.
Ecological Role: Land invertebrate. E. rosea is a source of food for numerous species. In Hawaii, it is preyed upon by the Norway rat (Rattus norvegicus), and the black rat (Rattus rattus). E. rosea serves as an important source of calcium for birds and is especially important during the breeding season when birds need a calcium-rich diet for eggshell formation. However, it is unclear whether E. rosea fills this role in Hawaii since the majority of Hawaiian birds are insectivorous.
Benefit(s): Of the fourteen snail species introduced to Hawaii for the biological control of A. fulica, only three have become established: Euglandina rosea, Gonaxis kibweziensis and Gonaxis quadrilateralis. Among these three, only
E. rosea has become invasive and has exerted a major ecological impact on the native Hawaiian snail fauna. The presence of E. rosea has probably played a role in keeping the populations of G. kibweziensis and G. quadrilateralis down. Since all three species occupy the same ecological niche in Hawaii, which lacks an indigenous predatory snail, competition for resources is inevitable. In such a competition, E. rosea (the larger, more adaptable species) would likely emerge victorious by consuming and outcompeting the other two species. However, the availability of these non-indigenous snails has probably also allowed E. rosea to exist in higher numbers than would otherwise be possible.
Threat(s): Currently, the greatest threat to terrestrial snails in Hawaii has been the exotic rosy wolfsnail. The native snail fauna of the Hawaiian Islands is rapidly disappearing. The terrestrial snail fauna consists of 11 families, most of which have suffered considerable extinction. The native land snails affected include: the family Amastridae, endemic to Hawaii, only ten species of the original 300 remain; in the genus Carelia, all 21 species endemic to Kauai are believed to be extinct; in the genus Achatinella, 80 percent of the 41 species found on Oahu have become extinct; 50 percent of the species in the genus Partulina, found on Molokai, Maui, Oahu, Lanai and the Big Island of Hawaii have been devastated.
Since its introduction, the rosy wolfsnail has become an out-of-control invasive that has developed a taste for the island’s native snail species, driving several to extinction and pushing the entire genus Achatinella onto the US endangered species list. Human activities have further introduced E. rosea to other islands, with similar devastating effect on the local snail fauna. In Mauritius, 24 of 106 endemic snails became extinct, and on the island of Moorea in French Polynesia, E. rosea was responsible for the extinction of seven endemic snails in the genus Partulina.
Control Level Diagnosis: Highest Priority. According to the Global Invasive Species Database, E. rosea is considered one of the world's 100 worst invaders. The presence of E. rosea has been strongly linked to the extinction and decline of numerous snail species in every area where it has been introduced.
Control Method: Conservationists are working to prevent the further spread of E. rosea. Exclosures have been built in Hawaii and French Polynesia to prevent E. rosea from attacking native tree snails. These barriers are somewhat successful but require constant monitoring and maintenance. A toxic bait using snails from the genus Pomacea is being tested in Hawaii.
Cook, Anthony. Feeding Behavior of Euglandina. The Malacological Society of London and the Linnean Society of London. January 21, 1999.
Cowie, Robert H., 1998. Patterns of Introduction of Non-indigenous Non-marine Snails and Slugs in the Hawaiian Islands. Biodiversity and Conservation 7, 349-368.
Cox, George W., 1999. Alien Species in North America and Hawaii. Island Press, Washington, DC.
Howarth, Francis G., 1991. Environmental Impacts of Classical Biological Control. Annual Review of Entomology 36, 485-509.
Loope, Lloyd L., The Effect of Introduced Euglandina Snail on Endemic Snails of Moorea, French Polynesia. September 27, 2002. US Geological Survey Publications.
Euglandina rosea (Ferussac 1821) - Rosy Wolfsnail. October 20, 2002.
Global Invasive Species Database. Euglandina rosea (land invertebrate).
Global Invasive Species Programme. Case Study 3.1: Euglandina rosea.
Photos of Euglandina rosea courtesy of the Jacksonville Shell Club.
US distribution map of Euglandina rosea, photo of Pomacea bait and Hawaiian Tree Snails courtesy of Florida State University.