Stock Island Tree Snail

1 The Stock Island tree Snail (Orthalicus reses, notincludingnesodryas) is an arboreal Snail inhabitingthe hardwood hammocks of the Florida Keys. It waslisted as threatened because of population declines, habitatdestruction and modification, pesticide use, and over-collecting. Snail collecting in South Florida has beenpopular for many years, and although the Stock Island treesnail lacks the vibrance and radiance of some of the otherintricately colored snails , it has not escaped intensecollecting pressures. In addition, it has not escaped thepressures of destruction of its habitat due to residential andcommercial construction activities.

2 The Stock Island treesnail historically occurred on the islands of Stock Islandand Key West, both from which it has been largelyextirpated from its historic range. In response to the loss ofhabitat and decline in the number of snails on Stock Island ,collectors have moved snails and introduced them to areasoutside of their historic range. The few remainingpopulations have continued to decline as a result of furtherhabitat loss and other account represents a revision of the existingrecovery plan for the Stock Island tree Snail (FWS 1982).

3 DescriptionThe Stock Island tree Snail is a large, conical Snail attainingapproximately 45 to 55 mm in length. The external groundcolor is white to buff, with three poorly developed spiralbands and several flame-like purple-brown axial stripesthat stop at the lower of the spiral bands (Deisler 1982).The thickness of the shell varies, but is usually morelightweight and translucent than other species ofOrthalicus(Pilsbry 1946). The axial stripes are typicallynarrower than their whitish interspaces and do not fork nearthe upper suture.

4 There are two to three white apicalwhorls. The last whorl contains two to four darker brownStock Island tree SnailOrthalicus resesPage4-767 Federal Status:Threatened (July 3, 1978)Critical Habitat:None DesignatedFlorida Status:EndangeredFigure 1. Distribution of the Stock Island treesnail; this species is endemic to only the FloridaKeys portion of Monroe Plan Status:Revision (May 18, 1999)Geographic Coverage:Rangewidegrowth-rest varices. The columella and parietal callus are white or faintchestnut brown. This species is distinguished from O.

5 R. nesodryasby its lightercolor pattern of the apical whorl, columella, and parietal callus. Thesecharacteristics are chestnut-brown or darker in O. Stock Island tree Snail is a subspecies of the genus Orthalicus, a group oflarge, arboreal pulmonate snails in the family Bulimulidae. Orthalicusoccursprimarily in Central and South America. Two species occur in North America,O. reses and O. floridensisPilsbry, both of which are restricted to SouthFlorida. Orthalicus reseshas two subspecies, resesand Stock Island tree Snail ( ) was first described by Say in 1830 basedon a Snail that was probably collected from Key West.

6 That specimen was lostand the species was later described by Pilsbry (1946) using a Snail collectedfrom Stock (1946) suggested the Stock Island tree Snail arrived in Florida fromCentral America and the Caribbean shortly after the emergence of the Floridapeninsula in the late Pleistocene. snails that were sealed to floating tropicaltrees may have been cast ashore on the Florida peninsula by high winds andhurricanes. This form of dispersal has been suggested for both Orthalicus andLiguus, but the exact origin of these species is still in question.

7 Craig (1972)suggested populations of Orthalicusarrived directly across the Gulf of Mexicofrom Central America, but the mode of transportation and whether dispersaloccurred on a single or multiple occasions was not known. No one knows whenthe Stock Island tree Snail arrived in the Lower , the Stock Island tree Snail was believed to have a very limiteddistribution, being found only in tropical hardwood hammocks on Stock Islandand Key West; although it may have been found in other hammock areas in theLower Keys. Their distribution has since been artificially extended bycollectors who have introduced them to Key Largo and the southernmost partsof the mainland.

8 Orthalicus reses nesodryashas a broader range, distributedthroughout the Keys from Sugarloaf Key north. Orthalicus floridensisis theonly Orthalicus species to occur naturally on the mainland, and is also foundin the , the Stock Island tree Snail occurred exclusively in hardwoodhammocks of the Keys. The Stock Island tree Snail survives best in hammockswith smooth-barked native trees that support relatively large amounts oflichens and algae. In the Keys, Orthalicusis limited to the higher portions ofthe islands that support hammock forests (minimum elevations of 5 to 11 feet).

9 Page4-768 Stock Island tree SNAILM ulti-Species Recovery Plan for South FloridaLower Keys hammocks consist of thick forests of tropical trees and shrubswhich grow in limestone, marl, and calcareous sand soils. Canopy trees includeblack ironwood (Krugiodendron ferreum), gumbo limbo (Bursera simaruba)Jamaican dogwood (Piscidia piscipula), mahogany (Swietenia mahagoni),pigeon plum (Coccoloba diversifolia), poisonwood (Metopium toxiferum), andstrangler fig (Ficus aurea). Hammock understory contains torchwood (Amyriselemifera), milkbark (Drypetes diversifolia), wild coffee (Psychotria nervosa),marlberry (Ardisia escallonioides), stoppers (Eugeniasp.)

10 , soldierwood(Colubrina elliptica), crabwood (Gymnanthes lucida), and velvetseed (Guettardascabra).Larger trees are more likely to support more Stock Island tree snails thansmaller trees probably because they provide the snails with an increased surfacearea for foraging (Deisler 1987). It is not known if Stock Island tree snails prefercertain tree types or species (Deisler 1987); however, Voss (1976) suggested treesnails generally prefer trees with smooth bark over trees with rough bark,because it would require less energy to crawl over smooth bark.