These enemies start very small and will eventually level up if left alone. They start as Larval Varkids, then go to Adult Varkids, then to Badass Varkids and eventually Super Badass Varkids. They will form cocoons and morph into the more dangerous versions, but they are vulnerable during the transition and can be killed in a few shots.
Larval Varkids have a stinger, similar to scorpions, that they use to defend themselves; this stinger is their weak point. Adult Varkids attack from the air, spitting corrosive balls at you; they are highly susceptible to fire. Badass Varkids are heavily armored and attack with their pincers; a corrosive weapon will be extremely helpful against these.