Adult fleas take blood from various kinds of mammals and birds but spend considerable time off the host. Their bodies are compact with flattened sides, permitting them to move rapidly among the hairs of the animal on which they are parasites. Their legs are well developed for rapid locomotion. Because they are minute and their bodies are hard, it is almost impossible to kill fleas by crushing them between the fingers. Different people have differing reactions to flea bites.
Some people are immune to the bites, are unattractive to fleas, or both.
Others are highly sensitive and attractive to fleas. In a flea-infested household, one or two individuals may be aware of and show severe irritation from bites. Other members of the family may not realize that fleas are present. Women and prepubescent children seem to be most attractive to fleas. Flea bites are most common on the legs, particularly around the ankles, but on small children the bites are likely to occur anywhere.