The typical flea is usually less than one-eighth of an inch long. Its smooth body is covered with a hard outer skeleton, and extending along the back are several rows of backward-pointing bristles and spines. Unlike the bodies of most insects, the flea's body is flattened from side to side, enabling it to move easily and quickly through hair or feathers. Fleas can leap long distances because of their strong slender legs. Some fleas, for example, can jump higher than 7 inches and farther than 13 inches.
Not all fleas have eyes. When present, however, the eyes are simple. Fleas also have a pair of short segmented antennae and sharp mouthparts adapted for piercing and sucking. Many fleas can pierce a host's skin and fill themselves with blood in a few seconds.
Usually each kind of flea attacks only one kind of animal. If the usual hosts are not available, however, most fleas readily attack other animals. For example, the cat flea (Ctenocephalides felis) also attacks dogs, man, and rodents, and the human flea (Pulex irritans) often attacks pigs. Only adult fleas suck blood. Although they usually feed once a day, some, such as the human flea, can live for several rnonths without eating. Most fleas leave their host after feeding and live in the host's nest or surroundings. Later they again attack the same host or find another. However, some fleas remain attached to their host. For example, stick-tight fleas (Echidnophaga gallinacea) often gather in clusters on the heads of chickens, cats, and dogs.
Some fleas can transmit serious diseases to man. The oriental rat flea (Xenopsylla cheopis) is the chief carrier of the bacteria that cause bubonic plague, an infectious and often fatal disease. The cat flea, which also attacks other animals, can infect man with a tapeworm common in cats and dogs. The chigoe (Tungo penetrans), also known as the sand flea, often burrows under the skin, causing serious ulcers.
