Snail on the Brink
The tiny palmetto pill snail lives in an equally tiny world — within about four feet of one warm spring at Palmetto State Park.
By Wendee Holtcamp
The palmetto pill snail (Euchemotrema leai cheatumi) lives a sheltered existence. The diminutive gastropod is small and roundish and prefers the shady undersides of palmetto fronds and the bark of hackberry trees. In the entire world, this endemic species thrives only at a single warm spring in Palmetto State Park. The 270-acre park is itself a novelty, the westernmost patch of dwarf palmetto (Sabal minor) thicket in a region surrounded by drier Central Texas vegetation.
“It became a high priority in terms of species that need monitoring,” says Leeann Linam, who helps coordinate the TPWD Texas Nature Tracker program. The federal government lists the snail as a species of concern, but it can’t be federally protected until more information becomes known about its natural history and ecology. Starting in 1999, volunteer teachers and students combed the state park to locate the tiny gastropods, to quantify the snail’s abundance and to determine if it preferred certain habitat types.
Volunteers scoured parts of the park, and in 235 sample plots found only 34 live snails and 35 shells containing dead snails over five years. They discovered that the snail flourished near the water’s edge on habitat blooming with wild iris and wild onion, but only in a very specific location — a permanent 81-degree spring-fed wetland maintained by a hydraulic pump built by the CCC in the 1930s. The snail was never found, dead or alive, more than four feet from this single locale. According to Barry Miller, manager of the Gonzales County Underground Water Conservation District, this temperature means the water emanates from a depth of roughly 600 feet, placing it near the bottom of the Carrizo aquifer, and the sulfurous odor in the water suggests some mixing with water from the lower-lying Wilcox aquifer.
Although this hydraulic-pump-maintained wetland seems somewhat artificial, at one time the entire region gushed with permanent spring-fed warm springs and mud boils, but they dried up by the 1970s. The neighboring Warm Springs Rehabilitation Hospital maintained a permanent fountain drawing water from the aquifers for many years. “It used to flow a tremendous stream,” says Miller.
Whether the snail exists elsewhere in the park remains unknown, but since Nature Trackers volunteers discovered that the snail prefers wetland edge habitat, more focused surveys can be undertaken. Although the student data can’t directly contribute to the federal listing process, it’s currently the main information local park managers have for habitat and species management.
A flood in 1998 heightened concerns about the importance of studying and protecting the critical habitat for this rare gastropod. “Those palmetto wetlands are a unique ecosystem in themselves, and the welfare of the snail is tied to the welfare of the wetlands,” stresses Linam.