Fleas are small insects that lack wings, and instead hop around for travel. They live as parasites on the bodies of mammals and birds. They have very short antenna, and in most cases they fit into grooves on the head.

Many fleas are bloodsucking and can transmit diseases such as bubonic plague. Others burrow into the skin of mammals and live there.

Fleas, unlike other parasitic insects, are not particular to feed on just one species. They can life away from the body of their host for a while and can find another host in the meantime.

The order Siphonaptera is divided into seven families, seperated by the characteristics of their heads and abdomen. These seven families are: Pulicidae, Ischnopsyllidae, Tungidae, Dolichopsyllidae, Hystrichopsyllidae, Malacopsyllidae, and Vermipsyllidae.