Florida Keys Tree Snail

Orthalicus reses is a snail with a large, conical shell that is approximately 45 to 55 mm in length. The thickness of the shell varies, but is usually more lightweight and translucent than other species of Orthalicus. The external ground color of the shell is white to buff, with three poorly developed spiral bands and several flame-like purple-brown axial stripes that stop at the lower of the spiral bands. The axial stripes are typically narrower than their whitish interspaces and do not fork near the upper suture. There are two to three white apical whorls. The last whorl contains two to four darker brown growth-rest varices. The columella and parietal callus are white or faint chestnut brown. The nominate subspecies Orthalicus reses reses is distinguished from the supposed subspecies Orthalicus reses nesodryas by the lighter color pattern of the apical whorl, columella, and parietal callus. These characteristics are chestnut-brown or darker in Orthalicus reses nesodryas.

Henry Augustus Pilsbry suggested, in 1946, that Orthalicus reses reses arrived in Florida from Central America and the Caribbean shortly after the emergence of the Florida peninsula in the late Pleistocene. Snails that were sealed in place on floating tropical trees may have been cast ashore on the Florida peninsula by high winds and hurricanes. This form of dispersal has been suggested for both Orthalicus and Liguus, but the exact origin of these species is still in question. In 1972, Craig suggested that populations of Orthalicus arrived directly across the Gulf of Mexico from Central America, but the mode of transportation and whether dispersal occurred as a single event or multiple events was not known. No one knows when Orthalicus reses reses arrived in the Lower Keys. Historically, the Stock Island tree snail was believed to have a very limited distribution, being found only in tropical hardwood hammocks on Stock Island and Key West; although it may have been found in other hammock areas in the Lower Keys. The distribution has since been artificially extended by collectors, who have introduced them to Key Largo and the southernmost parts of mainland Florida. Orthalicus reses nesodryas has a broader range, occurring throughout the Florida Keys from Sugarloaf Key north. …

Orthalicus reses reses snails are active mainly during the wet season, i.e. May through November, during which time breeding, feeding, and dispersal takes place. Dry periods (December through April) are spent in aestivation, during which time the snail forms a tight sealed barrier between the aperture and a tree trunk or branch. Snails secrete this mucus seal (an epiphragm) that cements their shell to a tree in order to protect them from desiccation during the dry period. Snails may come out of aestivation briefly to feed during dry-season rains, and also may go into aestivation during summer dry spells.