As a sequel to my first question, I have decided to ask another! Let's say, that these bugs have evolved to look completely like a mammal. Fur, skin, eyes, etc. What about their internal biology could distinguish them from a true mammal and reveal their bug origins? It probably wouldn't be obvious to the average person, but an avid insect-fan would be able to tell pretty quickly, especially considering these creatures are equipped with an endoskeleton.
