Mite Raknoids count for this, they're the little green ones that come out of the ground when you're farming minerals just to piss you off. Just kill them while being in the air when they spawn. They spawn in groups of three so you'll need to get four groups to get the achievement. They also seem to be random about spawning so I was just doing a lap around the starting area pond with the grinding pipes and killing them if/when I found them. Make sure you don't have a companion/sentinel with you to avoid them killing the Raknoids.