The cuckoo wasp is an example of an insect that rolls up defensively. The pillbug is an example of a crustacean that rolls up defensively.

As it turns out, there’s a Klingon animal that does roll itself up into a ball when in danger (that is, it pretends to be dead or inanimate or something). It’s called a woSwa'. There’s also a bug that does the same thing, and it’s called a woSwa' ghew, suggesting that the rolling-up characteristic of the woSwa' is one of its defining features.