Werebat
Explorer
I didn't know anything about mites, they look like a good threat for the PCs when they are just starting.
Yeah, just be wary of giving them swarm allies. Many/most low level parties can't do anything to swarms other than run away from them.
I used mites as low level adversaries in my current campaign... They were living in a cave infested with fire beetles and they had trained/tamed some flash beetles as well as a few medium sized giant spider mounts. It worked out pretty well.