98% of fleas in domestic premises are cat and dog fleas. There are dozens, or perhaps hundreds of different types of fleas with specific hosts. A flea needs a blood meal from its host before it can reproduce. This does not stop the flea from biting other animals besides its host. Only a tiny proportion of the flea population is on the host at any time, they hop on, feed and hop off.

After each blood meal from its host, the adult flea lays several hundred eggs in a number of batches. Eggs hatch into larvae, which are not blood suckers, they feed on general organic debris. Larvae are legless, white in colour and covered in large bristles. When they are about 5mm they pupate and they remain in the pupal state until they are stimulated to hatch. Triggers for hatching are movement, carbon dioxide concentration and heat, but the most important is movement. This mechanism ensures that they only hatch when there is an animal to feed on.

There is a rush of newly hatched fleas where infected premises have been left empty for a while, such as when you return from holiday. This problem becomes greater when properties are empty for extended periods when awaiting sale. Flea treatment uses 2 types of insecticide, one kills the adult fleas and the other prevents eggs hatching. Each has a residual effect so that fleas subsequently hatching are also killed, but persistent insecticides, such as DDT, are banned. All insecticides have to break down after a few months, so the longer a property is left unoccupied, the greater the risk of the residual insecticide being unable to cope.