Crickets, from the Gryllidae are usually heard chirping before they are ever seen. Male crickets are the only ones that chirp. More than 900 species of crickets are described; the Gryllidae are distributed all around the world except at latitudes 55° or higher, with the greatest diversity being in the tropics. They occur in varied habitats from grassland, bushes, and forests to marshes, beaches, and caves. Crickets are mainly nocturnal, and are best known for the loud, persistent, chirping song of males trying to attract females, although some species are mute. The singing species have good hearing, via the tympani (eardrums) on the tibiae of the front legs.. They have long antennae and somewhat flattened bodies. They tend to be nocturnal, and they are harmless to humans.