Senior Seminar 2002
Introduced Species in Hawaii

Mollusca
Snails

   Euglandina rosea    
Common Name: Rosy Wolfsnail

E. rosea
Photo courtesy of:  Jax Shells

Introduction
Before Western discovery of the Hawaiian Archipelago in 1778, only 2 or 3 species of snails had been introduced to the islands. In the 19th century, on average, one species was introduced each decade. In the 20th century the rate of introduction rose to four species per decade; with the exception of the 1950s when the rate was even higher due to the intentional introduction of biocontrol agents for a pestiferous snail species Achatina fulica. The biocontrol agents used were dominantly African species (Cowie 1998). Euglandina rosea was one of these biocontrol agents, and its introduction caused the extinction of the endemic tree snail Achatinella mustelina.

Description
Euglandina rosea
E. rosea is a predaceous snail that eats land and freshwater slugs and snails, including A. fulica and A. mustelina (Kinzie 1992, Harrington et al. 2001). It eats all sizes of A. mustelina (Hadfield et al. 1993). E. rosea finds its prey by following the slime trail left behind as the animal moves. This ability is not dependent on E. rosea's sense of smell, but instead on "lip tentacles". These elongated lips are essential to E. rosea's ability to follow trails, after surgical removal of lips, Cook (1985) found the snail unable to follow a slime trail. The ability to follow a trail develops within 1-3 months after hatching, with exposure to trails. E. rosea will follow a slime trail for two reasons: to find prey or to find a mate. It is able to distinguish between trails left by prey or conspecifics and by prey of lesser or greater desirability (Harrington et al. 2001). After copulation, following a conspecific's trail is decreased. After feeding, following of a prey trail decreased, recovering after 9 days, with feeding also resuming after this time (Cook 1985). The ability of E. rosea to follow a trail is dependent on the conditions of the trail. Cook (1985) found E. rosea's ability to follow persisted if the trail was kept dry for 24 hours, however if the trail was soaked in water for 30 minutes, the predator's ability to follow was diminished.

E. rosea feeds on snails by sucking the contents out of the shells or by swallowing the prey whole, earning it the nickname "cannibal snail" (ABI 2001). Cook (1989) found that when offered a wide variety of prey sizes, E. rosea preferred small prey and often swallowed them whole. Muragaki and Deguchi (1987) observed feeding behavior of E. rosea on A. fulica and found the largest prey size to be 49 mm in length, while the average size of prey was 10-30 mm in length, mainly juveniles. The mean prey consumption rate was .32 prey individual per day per predator (Muragaki and Deguchi 1987). As size of prey increased, handling time increased exponentially. However, handling time decreased exponentially as the size of the predator increased (Cook 1989).

      
E. rosea
Photo courtesy of: Jax Shells

Achatinella mustelina
Common Name: The Oahu Tree Snail
A. mustelina is endemic to the Hawaiian Islands, inhabiting only a short mountain range on Oahu. Its life history is characterized by slow growth, a late maturity of 3-5 years, fecundity of 7 offspring per adult per year, and a life span of over 10 years. Young are born live at about 4.6 mm in length (Hadfield et al. 1993), grow an average of 2 mm. a year, and reach terminal growth at 18.44 mm. (Hadfield and Mountain 1981). Hadfield and Mountain (1981) found maturity to occur at 6.9 years old. Reproductive maturity occurs after maximum size is reached.

   
  A. mustelina
Photo courtesy of:  http://www.weichtiere.at/Mollusks/Schnecken/land/achat.html

Achatina fulica
Common Name: Giant African Snail
A. fulica is a pest species because it destroys crops and is a threat to human health and safety (Howarth 1985). It has been introduced to many parts of Asia, including Taiwan and Japan and is found on many islands in the Pacific and Indian Oceans, and the West Indies (Takeuchi et al. 1991).

           
A. fulica
Photo courtesy of: Stanford University & Honolulu Zoo

Geographic Range
E. rosea is native to Latin America and the southeastern United States (ABI 2001). In addition to the Hawaiian Archipelago, E. rosea has been introduced as a biocontrol agent to more than 20 other group of islands (ABI 2001) in the Pacific and Indian Oceans (Cowie 1998) and Polynesia (Murray et al. 1988).

United States Distribution Map for E. rosea
Photo courtesy of:  Association for Biodiversity Information

Vectors
The origin of these introduced species changed throughout time. Early arrivals came from the Pacific, and later arrivals came largely from America, with the latter part of the 20th century bringing introductions from Europe. In total, 81 species of snails and slugs have been introduced to the Hawaiian Islands, 33 are established: 12 of which are freshwater and 21 of which are terrestrial species (Cowie 1998).

Why E. rosea is successful
Being a generalist, endowed with behavioral plasticity, has enabled E. rosea to be successful on the Hawaiian Islands. With a broad diet, this species is able to exploit a wide range of prey species (Kinzie 1992).

E. rosea eats all sizes of A. fulica. In comparison, rats who also feed on A. fulica prey only on the large snails. In the long-run, E. rosea may destroy its food source, whereas the rats will leave an area before all the snails are eaten, enabling the population to rebound and reestablish itself (Hadfield et al. 1993).

Impacts
In the world, it is estimated over one hundred species are threatened or extinct as a result of the introduction of E. rosea (Clarke et al. 1984).

Intentional introduction of a generalist species can be especially harmful to native environments and native organisms because it has the potential to affect non-target organisms. This was the case with the purposeful introduction of E. rosea to the Hawaiian Islands to control A. fulica. The presence of E. rosea caused the extinction of the native, A. mustelina (Cowie 1998).
After the introduction of E. rosea to the island of Oahu, 15-20 native species of Achatinella snails have gone extinct in the past four decades (ABI 2001).

Following E. rosea's introduction to Pacific Islands, A. fulica has decreased in numbers as a result of both predation and the introduction of disases (Gerlach 2001).

After intentional introduction of E. rosea to the island of Moorea in French Polynesia for biological control of A. fulica (Clarke et al. 1984), endemic land snails of the genus Partula, have gone extinct in the wild (Murray et al. 1988). After its introduction to a single orange plantation, the original population of E. rosea spread to cover one third of the island. The rate of spread between 1980 and 1982 was approximately 1.2 km/yr (Clarke et al. 1984).

Partula snail
Photo courtesy of: The Wild Ones Animal Index

Management
Based on my personal research, there does not appear to be a concentrated effort aimed at the management of E. rosea populations in the Hawaiian Islands. Having been brought intentionally to the Hawaiian Archipelago, E. rosea has caused negative environmental consequences, yet there is apathy to rid the islands of this pest. This reluctance could be due to misinformation, as many field studies have cited the success of E. rosea in eliminating A. fulica. However, these studies did not take into consideration the other factors (disease, parasitism, and reproductive seasonality) that may account for the decline in the A. fulica population (Christensen 1984). For example, after E. rosea was introduced to Moorea as a biocontrol agent for A. fulica, the A. fulica population decreased. However, this decrease cannot be solely attributed to E. rosea as there are still A. fulica found in areas occupied by E. rosea. In addition there were parts of the island where the A. fulica population declined but no E. rosea were present.

Bibliography
Association for Biodiversity Information (ABI). 2001. Rosy Wolfsnail (Euglandina rosea). URL: http://www.natureserve.org/publications/least wanted/snail.html (2 Dec 2002).

Christensen, C. C. 1984. Are Euglandina and Gonaxis effective agents for biological control of the giant African snail in Hawaii? American Malacological Bulletin 2: 98-99.

Clarke, B., J. Murray, and M. S. Johnson. 1984. The extinction of endemic species by a program of biological control. Pacific Science 38: 97-104.

Cook, A. 1985. Functional aspects of trail following by the carnivorous snail Euglandina-rosea. Malacologia 26: 173-182.

Cook, A. 1989. Factors affecting prey choice and feeding technique in the carnivorous snail Euglandina-rosea ferussac. Journal of Molluscan Studies 55: 469-478.

Cowie, R. H. 1998. Patterns of introduction of non-indigenous non-marine snails and slugs in the Hawaiian Islands. Biodiversity and Conservation 7: 349-368.

Gerlach, J. 2001. Predator, prey and pathogen interactions in introduced snail populations. Animal Conservation 4: 203-209.

Hadfield, M. G., S. E. Miller, and A. H. Carwile. 1993. The decimation of endemic Hawaiian tree snails by alien predators. American Zoologist 33: 610-622.

Hadfield, M. S. and B. S. Mountain. 1980. A field study of a vanishing species, Achatinella mustelina (Gastropoda, Pulmonata), in the Waianae Mountains of Oahu. Pacific Science 34: 345-358.

Harrington, M. A., K. T. Clifford, K. Johnson, et al. 2001. In the carnivorous snail Euglandina-rosea prey trail recognition and following are learned behaviors dependent on nitric oxide. 31st Annual Meeting of the Society for Neuroscience, November 10-15, 2001. Society for Neuroscience Abstracts 27: 238.

Howarth, F. G. 1985. Impacts of Alien Land Arthropods and Mollusks on Native Plants and Animals in Hawai'i. P;. 149-179. In, Stone, C. P. and J. M. Scott. Hawaii's Terrestrial Ecosystems Preservation and Management.

Kinzie, R. A. III. 1992. Predation by the introduced carnivorous snail Euglandina-rosea ferussac on endemic aquatic lymnaeid snails in Hawaii. Biological Conservation 60: 149-155.

Muragaki, S., and K. Deguchi. 1987. Predation by the carnivorous snail Euglandina-rosea ferussac gastropoda mollusca on the giant African snail Achatina-fulica bowdich gastropoda mollusca. Research Bulletin of the Plant Protection Service Japan 23: 71-74.

Murray, J., E. Murray, M. S. Johnson, et al. 1988. The extinction of Partula on Moorea French Polynesia. Pacific Science 42 (3-4): 150-153.

Takeuchi, K., S. Koyano, and K. Numazawa. Occurence of the giant African snail in the Ogasawara Bonin Islands Japan. Micronesica (Suppl. 3): 109:116.

Designed by:  Shannon Marie Murphy                                Contact: murphsh@earlham.edu
Last revised: 8 December 2002