Dog flea (Ctenocephalides canis).
Siphonaptera is an order of small, wingless insects comprising the fleas. They are blood-sucking, external parasites on warm-blooded animals. Fleas have hard, laterally compressed bodies with many microscopic, backward-pointing spines. Their mouthparts are adapted for piercing their host and sucking up blood. Their powerful, bristly legs enable them to perform single leaps of more than 30 cm.
Flea eggs are laid in dirt or in the nest of the host; the whitish larvae feed on organic matter and the feces of adult fleas. The larvae spin cocoons as part of the metamorphosis into adults. Many species can live on more than one host species. Adults can feed for several weeks without feeding.
Fleas cause irritation and some carry diseases. The rat flea (Xenopsylla cheopsis), for instance, can transmit typhus and bubonic plague to humans. Length: 1 cm (0.4 in).