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Pennsylvania State University scientists said the tiny snails out-compete native snails and insects but aren't good fish food replacements for the native species.

"These snails have an operculum, a door that closes the shell", said Associate Professor Edward Levri at the university's Altoona, Pa., campus. "They can be out of the water for longer than other snails and when fed to fish, they are not digested and sometimes come out alive. This has a potential to alter the salmon and trout fisheries because they alter the food chain."

The snails can grow to about 1/4 of an inch, but are more commonly 1/16th to 1/8th of an inch in length, Levri said. In some Yellowstone National Park streams they reach population densities of 323 snails per square inch. But less dense populations are reported in the Great Lakes area.

The study that included undergraduates Warren Jacoby, Shane Lunen, Ashley Kelly and Thomas Ladson, was presented Wednesday by Levri during the Ecological Society of America's annual meeting in Milwaukee.

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