Stock Island tree snail: Orthalicus reses [not including nesodryas]
Genus/Species: Orthalicus reses
Common Name: Stock Island tree snail
Federal Status: Threatened
FL Status: Federally-designated Threatened
FNAI Ranks: G1T1/S1 (Critically Imperiled)
IUCN Status: Not ranked
The Stock Island tree snail is a large snail that can reach a length of 2.2 inches (5.5 centimeters). Its thin shell is white to light brown with three brownish to purple horizontal stripes that surround the shell. Numerous narrow brownish to purple stripes can be found stretching vertically on the shell surface. The species also has a white inner shell spiral and shell tip (Florida Natural Areas Inventory 2001).
The diet of the Stock Island tree snail consists of the epiphytic (growing on the surface of a plant) lichens, fungi, and algae on their host tree (U.S. Fish and Wildlife Service 1999, Forys et al. 2001).
Stock Island tree snails are hermaphrodites (have both male and female reproductive organs). They mate and nest during the late summer and early fall months concurrently with the wettest part of the rainy season (U.S. Fish and Wildlife Service 1999). Nests are constructed in the humus of soil – the area of soil where carbon has reached maximum stability. Fifteen eggs per clutch are laid, which can take 24 to 105 hours to lay. Eggs hatch during the spring when the rainy season begins. Stock Island tree snails begin nesting at two to three years of age (Diesler 1987).
Habitat and Distribution
The Stock Island tree snail inhabits host trees in tropical hardwood hammocks. Important host trees include poisonwood (Metopium toxiferum), pigeon plum (Coccoloba diversifolia), Jamaican dogwood (Piscidia piscipula), strangler fig (Ficus aurea), and gumbo limbo (Bursera simarouba) (Florida Natural Areas Inventory 2001). This species is endemic to Stock Island and Key West in the Florida Keys, but went extinct in its native range in 1992. Several small populations remain, however, only in locations where the snail had been introduced outside of its historic range (U.S. Fish and Wildlife Service 1999, Forys 2001).
Habitat loss and modification is the main threat to the Stock Island tree snail. Increased urban development in the Florida Keys has caused habitat destruction, fragmentation, and degradation to the Stock Island tree snail’s primary habitat. Fragmentation may cause destruction to the microclimate (small atmospheric zone that has a different climate than its surrounding area), which is important for reproduction, feeding, and dwelling. Natural disasters (e.g., hurricanes) are a serious threat to the species, as its limited range could result in complete extinction during a single disaster event. Pesticide use near snail habitat can result in the altering of its reproduction, feeding, or the death of the snail. The increased collection of snails can cause a decline in population. Potential natural threats include predation from raccoons, birds, black rats, and fire ants (U.S. Fish and Wildlife Service 1999). Mortality from fire ants has been implicated as one of the most likely causes of the snail’s recent decline and extinction from its historic range (Forys et al. 2001).
Conservation and Management
The Stock Island tree snail is protected as a Threatened species by the Federal Endangered Species Act and as a Federally-designated Threatened species by Florida’s Endangered and Threatened Species Rule. Following an earlier version, a revised Federal Recovery Plan for the Stock Island tree snail was included in the Multi-Species Recovery Plan for South Florida (U.S. Fish and Wildlife Service 1999). The snail’s status was recently re-evaluated and found to still warrant Federal listing as Threatened (U.S. Fish and Wildlife Service 2009).
-Federal Recovery Plan
Other Informative Links
Florida Natural Areas Inventory
U.S. Fish and Wildlife Service Species Profile
U.S. Fish and Wildlife Service South Florida Multi-Species Recovery Plan
Printable version of this page
Florida Natural Areas Inventory. 2001. Field guide to the rare animals of Florida. http://www.fnai.org/FieldGuide/pdf/Orthalicus_reses_reses.pdf
Deisler, J.E. (1987). The ecology of the Stock Island tree snail, Orthalicus reses reses (Say).Bulletin Florida State Museum Biological Science 31(3): 107-145. Gainesville, FL.
Forys, E.A., A. Quistorff, C.R. Allen, and D.P. Wojcik. 2001. The likely cause of extinction of the tree snail Orthalicus reses reses (Say). Journal of Molluscan Studies 67: 369-376.
U.S. Fish and Wildlife Service. 1999. South Florida multi-species recovery plan. Southeast Region, Atlanta, Georgia.
U.S. Fish and Wildlife Service. 2009. Stock Island tree snail (Orthalicus reses (not including nesodryas)). 5-year review: summary and evaluation. U.S. Fish and Wildlife Service, Southeast Region, South Florida Ecological Services Office, Vero Beach, Florida.
Image Credit Photo courtesy of Dr. Dale R. Jackson, FNAI