James Cheshire writes,
"If only a single specimen of a foreign species was obtained for study,
could it do any damage if it escaped?"

Yes, (1) if the snail were pregnant, (2) if it interbred with local snails,
or (3) two collectors got their single specimens together to breed. Cases
(1) and (2) are not even rare, and though I can't remember an example of
(3), I would rather be safe than sorry.

Andrew K. Rindsberg
Geological Survey of Alabama