These... bugs? i guess? are People that (after a nuking on america) ate irradiated peanut butter
the rest of the humans were enslaved to MAKE peanut butter eventually there was a peanut shortage and the gronkles had to help. And naturally after they learned they had no use for humans therefor they killed them (except for the slave here and there) (Gronkles always eat peanut butter... and sometimes other animals but mostly peanut butter)

This is my skin entry (I am mostly going for originality here i was stumped on what to do so i did something random and apocalyptic)