I think is should be Piranha.
Theme of Ambush sounds a bit weird. I don't see Piranhas really ambushing anyone, plus it doesn't really describe the ability effect. Swarm is much close to what it does, but that's already taken by Scarabs.
But the mechanics fir the theme pretty well, although I personally would like to see this mechanic as a 
card called "Pack Wolf" because it fits better to wolves who hunt as a group and have a clear strategy that makes them dangerous. Pirahnas lack the intelligence to work as a team imo.
Yes, "ambush" is better for cards like pack wolf, I know that card, but I've found this about Piranha:
"The piranha is a gregarious fish, living in very many groups that sometimes come to populate whole stretches of river."
and
"The danger comes from the number of piranhas, a medium-large flock of several hundred individuals in a few minutes can strip the flesh off a sheep or a horse, and while going around it seems to literally boil the water."
Sorry if translation is not perfect. 1 Piranha is not so dangerous, but they can devour an horse when are many, and it's a fish about 30cm
"Working as a team" is not linked with intelligence, you can think to ants for example.
Name of skill could be something like "shoal"?
