West Sussex Pest Clear

Pest Control

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Behaviour and Biology

Adult fleas are normally 1-4mm long and brownish in colour. Fleas do not have wings but they do have very powerful legs and can jump large distances. Female fleas can live up to 2 years and can lay 25 eggs a day.

Where do they live?

Adult fleas live exclusively as parasites of warm blooded animals such as cats, dogs and humans. The eggs are slightly sticky and are laid on hair, bedding or clothing of the host. Carpets provide a relatively undisturbed environment for fleas to breed, they can also live in cracks and crevices of bare floors.

What do they eat?

Adults feed on the blood of the host animal (cat, dog, human). The larvae feed on the droppings of the adults.

Pest Status

Fleas are regarded as a 'nuisance pest' rather than a 'public health pest'. They are mainly regarded as pests because of their bites. Not all people are affected by flea bites, but for those who are, they can cause severe irritation.

Fleas are holometabolous insects, going through the three life cycle stages of larva, pupa and imago (adult). The flea life cycle begins when the female lays after feeding. Adult fleas must feed on blood before they can become capable of reproduction. Eggs are laid in batches of up to 20 or so, usually on the host itself, which easily roll onto the ground. As such, areas where the host rests and sleeps become one of the primary habitats of eggs and developing fleas. The eggs take around two days to two weeks to hatch.


Micrograph of a flea larva.

Flea larvae emerge from the eggs to feed on any available organic material such as dead insects, feces and vegetable matter. They are blind and avoid sunlight, keeping to dark places like sand, cracks and crevices, and bedding. Given an adequate supply of food, larvae should pupate within 1-2 weeks. After going through three larval stages they spin a silken cocoon. After another week or two the adult flea is fully developed and ready to emerge from the cocoon. They may however remain resting during this period until they receive a signal that a host is near - vibrations (including sound), heat and carbon dioxide are all stimuli indicating the probable presence of a host.

Once the flea reaches adulthood its primary goal is to find blood - adult fleas must feed on blood in order to reproduce. Adult fleas only have around a week to find food once they emerge, though they can survive two months to a year between meals. A flea population is unevenly distributed, with 50 percent eggs, 35 percent larvae, 10 percent pupae and 5 percent adults. Their total life cycle can take as little as two weeks, but may be lengthened to many months if conditions are favorable (that is, unfavorable for the fleas). Female fleas can lay 500 or more eggs over their life, allowing for phenomenal growth rates.


Flea "dirt" in the fur of a cat is actually excess blood from the host consumed by the adult flea and passed as feces.


The environment should be treated with a fogger or spray insecticide containing an insect growth regulator, to kill eggs and pupae, which are quite resistant against insecticides.