The easiest one first, probably. Here are the needed animations for them:
Worm: Move: it lurches itself forward like a slug and its spikes move a little.
Attack: I dunno what you want its attack to be.
Mite: Move: A simple leg-moving animation.
Attack: It half-jumps forward and chomps its jaws together.
Spider: Move: something like this:
http://www.uark.edu/~dksander/spideran.gif only all the legs move
Attack: It rears up and chomps with its fangs
Scorpion: Move: a "scuttling" animation, all legs move quickly up and then down, then to the side a little, like a crab
Attack: It rears back and swings its tail down, then backs up and clacks its claws.
I really hope these are possible, but it'd need a very talented animator...