Fleas are able to jump over eight inches, which is roughly the equivalent of a human jumping over the Statue of Liberty. Specialized anatomical structures allow them to attach to the skin of their hosts, but they pass easily from one host to another. Consequently, fleas can transmit a number of diseases. Most notably, the flea is responsible for transmitting the Black Death, bubonic plague, which killed a quarter of the population of Europe during the Middle Ages. Today the flea is known to transmit tapeworm and haemobartonellosis, a blood disorder that can be fatal to cats.
Serious infestations can cause severe inflammation, intense itching and even anemia.
Also, a number of pets, as well as people, have allergies to flea saliva that can result in rashes and hair loss. Eggs are laid on the body of the host animal, but since they aren't sticky they can drop in any number of places. The larva resembles a small legless caterpillar and it feeds on dried excrement, dried bits of skin, dead mites, dried blood, and other organic debris. Fecal matter from the parent flea is essential to the successful metamorphosis of some species of flea larvae. During this time the parent flea consumes a great deal of blood, up to 30 times its own weight, to produce a large quantity of feces for its larvae.