The most prevalent species of flea, is the Cat flea. The cat flea is a small insect about 1-2mm long. They vary in color, but most commonly are a reddish-brown. The cat flea’s key host is the domestic cat, but will also feed on dogs. A few fleas on adult dogs or cats effect very little harm unless there is an allergy to substances in saliva. Smaller animals with large infestations may suffer from dehydration from loss of bodily fluid. Cat fleas also may be to blame for disease transmission through humans, and have been allegedly connected to plague. Cat fleas can spread other parasites and infections to dogs and cats and also to humans. The most prominent of these diseases is lyme disease.