Cazador, radscorps bloatflies, radroach, mantis, fire ants, etc... they are all freaking big. Why not have some tiny-sized mutant insects that is more to likeness, and they should be dangerous as their bigger cousins since they are so small that it would be hard to hit the swarm with guns.

How about we use the suggestions topic ==> http://www.gamesas.com/topic/1401202-fallout-4-speculation-suggestions-and-ideas-thread-79/

Yep, use the linked thread for now