What are the grey bugs attracted to water multi legged roll into a ball when touched?

<quote> It's called a roly-poly. <quote>

Actually, it's called a pillbug or, the scientific name, is Armadillidiidae and it's in the family of woodlice. Because they roll into a ball when threatened many have called them roly-polies or potato bugs. However, it's a common mistake as these are not bugs at all but they're actually crustacean much like shrimp.

http://en.wikipedia.org/wiki/Pillbug

http://insects.about.com/od/isopods/a/10-facts-pillbugs.htm