Explain why a pet may have signs of FAD when no fleas are present. Flea allergy dermatitis is a type of hypersensitivity to flea bites. This is one of the most common skin diseases of dogs and cats. Flea biology and flea cycle Fleas are bloodsucking insects of mammals and birds. The have a chitin exoskeleton and 3 pairs of legs.
Fleas are laterally compressed wingless insects.
The wingless condition has been an adaptation to the parasitic life since the wings can get tangled in the host's hair. Fleas have strong jointed legs. Fleas can jump the equivalent of a man jumping 1000 feet. They can tolerate frozen temperatures and enormous pressure. Most species are variably host specific.