Fleas bite humans to obtain blood, their source of energy and nutrients, states the Illinois Department of Public Health. The human flea prefers humans and pigs, but humans are also bitten by other species of flea such as cat fleas and rat fleas. While different species of flea prefer to prey on different species, they can be easily transferred to other species in close proximity. In the United States, cat fleas bite humans the most often.
Fleas often bite more than once, testing different areas before selecting a site for feeding, explains the Illinois Department of Public Health. This often results in a line or cluster of itchy red marks on the skin around 30 minutes after the bites occur. Sensitive individuals may also experience raised bumps within 24 hours after the bites occur. Cat and dog fleas do not transmit diseases to humans through these bites, but rat fleas sometimes do; rat fleas can transmit bubonic plague and murine typhus to humans.
Young fleas stealthily ambush humans and other animals to feed on them, often using plants to gain a higher vantage point, according to the Illinois Department of Public Health. Fleas are very powerful jumpers for their size and can cross a distance of up to a foot. The flea attempts to bite as soon as it makes contact with the host.