They have sucking mouthparts and long hind legs for jumping.
Many species are very annoying because of their bites, and a few act as vectors of disease.
Some people and pets are known to develop allergic reactions to flea bites. Fleas become pests when they get into our houses. Fleas in houses are usually linked with a pet or a visiting cat or dog. Wild animals have fleas also, and if such animals are living in the homes, fleas may become a problem. Flea problems often occur when the host animal has been absent for a period of time, such as when the family goes on vacation taking or boarding the pet.