More than 2,000 types of fleas parasitise mammals and birds. Dogs are most commonly inhabited by the Ctenocephalides felis (cat flea), more rarely by the Ctenocephalides canis (dog flea), and occasionally by the Pulex irritans and Pulex simulans (human flea), as well as by the Echidnophaga gallinacea (hen flea) and (hedgehog flea).
Fleas are wingless, laterally flattened insects around 1-6mm in length with a strong talus and piercing-sucking mouth parts. They are light to dark brown in colour and feed off the blood of their host animal.
The development of fleas progresses from the egg to three larva stages to the pupa and then the adult form. Female fleas take just a few minutes to inhabit the dog's blood and start to lay eggs after around 24-48 hours. During its lifespan of around 50-100 days, it lays on average 30 eggs per day. The eggs are mostly laid during the dog's rest period and fall out on its sleeping spot or other areas where it frequently rests. Within a few days, the eggs hatch and become larvae, developing over three stages into pupa. The larvae feed off cell material and flea excrement with undigested blood, which is released from the dog along with the eggs. The adult flea hatches from the pupa and seeks to inhabit the nearest dog as soon as possible. In unfavourable conditions, such as cooler temperatures, the pupa can survive in its cocoon for up to 50 weeks until hatching. In ideal conditions, the duration of the cycle from egg to adult flea is around two to four weeks. Adult fleas from C. felis and C. canis permanently live on their host; they occasionally cross over to other hosts, but don't stay in the surrounding area for a long time. The flea's youthful stages (egg, larva, pupa) live in the environment, the larvae hole up into hiding places such as under cushions and carpets, as well as gaps in the flooring.
Dogs can bring fleas into the home through contact with other animals. The conditions in a living space are ideal for the development of fleas, and they multiply rapidly in this environment. C. felis, the most common type of flea, is not picky in its choice of host animal: it has been found on over 50 different types of animal all over the world, as well as on humans.