The Quilted Melania, Tarebia granifera is a relatively small freshwater snail with an operculum ranging in size from 6-40mm, average of 25mm. The shell is elongate and spiraled with several rows of beads which gives the shell a "quilted" appearance. It's color is light to yellowish brown, often flecked with reddish-brown spots. The shell has between 7-11 whorls at adulthood. Maturity is reached, on average, 122 days after birth.
Ecological Threat: In addition to out-competing indigenous snails, the quilted melania also poses a health risk to humans and birds. The Quilted Melania is an intermediate host to various trematodes that can infect humans as well as birds.
Biology: While the snail is not known for its rapid migration actively, passive migration, be it via water currents or attachment to birds or other organisms, is a probable method of distribution for the Quilted Melania. This could lead to colonization events in naive habitats.
Once in a new habitat, the snail has proven to be an aggressive competitor with native species. This is enhanced by the snail being a parthenogenic species; that is, only a single female is necessary for reproduction. In fact, when males are present, they are are non-functional. In addition, these snails are oviparious meaning the eggs hatch within the mother, and juveniles exit into the environment through the egg pore. This could lead to greater fecundity and an increase in population size with few founding individuals, and would allow a single snail to potentially out compete a naive pond with her offspring. Parthenogenic species are often difficult to eradicate because mating is not necessary for reproduction.
These snails feed on rock algae, microorganisms, diatoms, but do not appear to damage aquatic plants.
History: It is uncertain when the quilted melania was introduced into the United States, but a detailed description of the biology of the snail was published by Tucker Abbott in 1952, and a introduction date of 1940 has been suggested. Researchers believe the main method of introduction was via the aquarium industry. Negligent aquarium owners probably dumped their tanks into freshwater systems which then led to the snail's establishment.
U.S. Habitat: The Quilted Melania is a freshwater snail that prefers:
-Riffles of shallow fast-moving freshwater streams (Very rapid water flow is usually avoided)
-Substrate consisting of small stones
-Thrives in both medium velocity and slow-moving streams
-Shallow areas most often occupying depths no greater than 4 feet (Usually found at depths of 1 foot or less)
-All natural water bodies
-Water exposed to direct sunlight seems to attract more snails than water shaded by vegetation.
Native Origin: India east to the Philippines and Hawaii, north to South Japan and south to the Society Islands.
U.S. Present: The Quilted Melania has established populations in Florida and Texas.
In Texas, the snail has established populations in the San Antonio River in Bextar County, Landa Park in New Braunfels, Comal County and the San Marcos River in Hays County, as well as many springs within that general vicinity.
Very often confused with the related Red-rimmed Melania, Melanoides tuberculatus. Often size is the only way to distinguish the two species, as shell patterns can overlap. Generally there are more red dots on the Red-rimmed Melania (hence the name), but there can still be reddish dots on the Quilted Melania as well.
While the snail has already established itself in Texas and Florida, as well as Puerto Rico, it appears that eradication may be an irreversible process. These snails cannot survive in water colder than 7 degrees Celsius (44.6 degrees Fahrenheit), and tend to prefer water warmer than 18 degrees Celsius (64.4 degrees Fahrenheit) which should limit its distribution abilities. The snail is, however, able to easily withstand diverse chemical, physical and biological conditions including water polluted with sewage treatment effluent, mud, silt, and detergents. Oddly, the snail has a low tolerance to salinity, and cannot survive water pH out of the 7.1-8.5 range.
Chaniotis, BR, Butler, JM, Ferguson, FF, and WR Jobin. 1980. Bionomics of Tarebia granifera (Gastropoda: Thiaridae) in Puerto Rico, an Asiatic vector of Paragonimiasis westermani. Carib J Sci. 16(1-4).
Abbott, RT. 1952. A study on an intermediate snail host (Thiara granifera) of the oriental lung fluke (Paragonimus). In: Proceedings of The United States National Museum. Vol 102(p.71-116).
David Rogowski - Texas Tech University - firstname.lastname@example.org