Flea

Fleas are small, laterally compressed, wingless insects which, as adults, are external parasites of mammals, including rodents and humans, and birds. As adults their mouthparts are adapted for piercing and sucking. Fleas can carry and transmit various allergies and disease that can be passed to humans when the flea bites. Fleas usually bite humans around the ankles and lower legs. Each bite produces a small, hard, red spot with a noticeable puncture wound. Flea populations usually reach their peak during late summer when the temperature and humidity rises.

Impact on Animal Health	Impact on Human Health

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Life Cycle

Adult

The adult flea is 1.5 - 4 mm long, depending on species. It is wingless, laterally flattened and brown in colour. The neck is short, as are the antennae that fit into a protective groove on the head when not in use. The eyes are not well developed and in some species including the house mouse flea Leptopsylla segnis eyes are totally lacking. Many species have combs or arrays of stiff bristles, that prevent the flea from being dislodged from the coat of the host and well developed hind legs adapted for jumping. Two notable exceptions to the adult jumping flea are the sticktight flea (Echidnaphaga gallinacea) which is a parasite of chickens and the sand flea or jigger (Tunga penetrans) which parasitises man and animals. The female of these fleas burrow into the skin of the host and remains attached for life.

Adult fleas feed by piecing the host's skin with their mouth parts and penetrating a capillary from which they suck blood, using one or more pumps to convey the blood to the gut. If undisturbed, feeding is complete in from 2-10 minutes. Female fleas take up about twice as much blood as males.

The adult flea has a maximum life span of approximately 18 months but on average they life for only 2-3 months.

The Egg

Flea eggs are smooth and white in colour. Most species lay two to six eggs per day and can lay hundreds over a lifetime. Eggs are normally laid in the host's sleeping and resting areas. When laid on the host, as is the case with cat and dog fleas, the eggs fall out of the hosts' coat, often at the hosts sleeping area. Eggs typically hatch in 3-5 days if humidity is above 70% and temperatures are between 18-26°C.

The Larvae

Flea larvae are blind and legless worms with circlets of hairs around each intersegmental division. The larvae go through three moults and when fully grown are approximately 4 mm in length. Flea larvae are usually intolerant of light and quite mobile. They feed on debris on the floor, typically in the resting quarters of the host. Adult fleas supplement this debris with undigested fecal blood.

The Pupa

The mature larva spins a whitish, ovoid cocoon incorporating debris into it. This resting stage allows the flea to survive long periods until stimulated to hatch by vibrations caused by the movement of the host. Pupae will not survive in low humidity (below 45% for the rat flea). In normal conditions the pupal stage last for one to three weeks.