The mouth of fleas is adapted for puncturing animal skin and sucking blood. Both male and female fleas suck blood. Fleas normally prefer the blood of domestic animals over that of humans, so it is not unusual for people to coexist with their pet and its flea population under normal conditions and be bitten only occasionally. However, when the preferred host is absent (likely, your pet!), a population of hungry adult fleas will accumulate. Hungry fleas will not discriminate between blood from pets and other animals and will attack almost any warm-blooded animal that strays near.

Cats and dogs scratch and bite themselves constantly when heavily infested. As a result, their skin is irritated and their coats become rough and unkempt. The initial irritation, itching and rash are caused by salivary secretions injected by the flea during feeding.

Several diseases may be transmitted by the bite of an adult flea, including plague and typhus. Rodents and pets are the most common sources of fleas and the diseases they carry. Flea voracious feeding behavior and their indifference of hosts increase the potential for fleas to transmit disease-causing organisms between humans and animals.