X-ray of a rusty crayfish (Orconectes rusticus) protecting her eggs. The crayfish protects her eggs by holding them under her tail until they hatch. The rusty crayfish is an invasive species. Rusty crayfish were spread by anglers who used them as fishing bait. As rusty crayfish populations increased, they were harvested for the regional bait market. Invading rusty crayfish frequently displace native crayfish, reduce the amount of aquatic plants and invertebrates, and reduce fish populations.