Mayfly Species Acerpenna pygmaea (Blue-Winged Olive)

Costal process: A bump or point sticking up from the front margin of an insect's wing, usually the rear wing of certain mayflies. It is sometimes called a costal projection.

Nymphs: The juvenile, underwater stages of mayflies, stoneflies, dragonflies, and damselflies and other aquatic insects whose juvenile stages are covered by hard exoskeletons. The word can also refer to the fishing flies which imitate these creatures, in which case it is used as a blanket term for flies imitating any underwater stage of an invertebrate (except for crayfish and leeches).