Your front legs get bigger and bigger, for grabbing, and then pointier, for stabbing, and then another gene error gives you the ability to make a venom! This rapidly leads to a hunting, killing, approach where you creep up on sleepy insects, stab them with some venom, and then carry them away to eat in a convenient dark hole.

This proves to be a very successful strategy, and in the last 400 million years you’ve hardly changed.

You are a centipede.