In Costa Rica we know it's May when we see the first "Abejón de mayo" (May beetle). These harmless beetles appear with the first showers of the year, which are normally in May. They are part of the Melolonthinae subfamily of the scarab beetles, a very diverse group; distributed over most of the world. During the day they hide under the soil to protect themselves from predators, and come out mostly during the night.
