Small (2mm) wingless insects, flattened side to side, red-brown with backwardly directed spines and legs designed for jumping. All adult fleas are parasitic on warm-blooded animals. Larval stages live in the nest of the host and feed on skin, feathers and, most importantly, the blood-rich faeces of the adult flea. When fully grown the larvae spin well camouflaged silken cocoons. When fully developed the adult waits within this until it detects the vibrations caused by a potential host. Only then does it emerge.
The complete lifecycle takes about a month in the summer. Adult fleas feed on blood. Their bites can cause intense irritation around the central bright red spot. Different people react differently to a bite, both in terms of degree of reaction and time taken to react.
The Cat Flea is by far the commonest species of flea and readily bites humans. The Human Flea and the Bird Flea are next in importance. Dog fleas are rare, although other species may become temporarily attached to dogs.