The adult cat flea is around 2-4mm long and a dark brown colour. The body is compressed laterally to make it easier for the flea to navigate in between hairs. It is capable of great jumping feats, with an average jumping distance of 20cm and an average height of 15-25cm. The adult flea is a permament parasite. It is very unlikely to jump from one pet to another, and  only survives 3-5 days in the environment Adult fleas take their first blood meal within 30 minutes, and breed within 48 hours. Females can lay up to 50 eggs/day for 50-100 days with an average of 20-30 eggs a day laid over a 2 month period. Fleas can live 100 days or more. 

Flea eggs are pearly-white and oval-shaped. They are about 0.5mm long. Flea eggs are not sticky, so after being laid they fall from the fur and accumulate in areas where the host spends most of their time. Sleeping and resting areas in particular are likely to become heavily contaminated. 

Once hatched, flea larvae will seek a dark, humid area to hide in while they develop. They can move up to 20cm to do this, and will often take up residence at the base of carpet fibers, under furniture and in cracks in the flooring. Larvae feed mostly on flea poo and other organic debris. Larvae are very sensitive to dessication (drying out), and will die if exposed to relative humidity levels of less than 33%. Flea larvae take 5 days to 3 weeks to develop into pupae depending on environmental conditions. 

The third larval stage matures into a pupa, which is usually covered by a silk cocoon. The cocoon is whitish, about 0.5mm long and is covered in sticky silk fibres. These pick up debris from the environment and help to camouflage the pupa. The pupa metamorphoses into an adult in 6 days to several weeks. At this stage it can do one of two things: if there are animals around, it will hatch as an adult and try to find a host. If there are no animals around, then they can remain in the cocoon as a pre-emerged adult.

Now that you know a little more about fleas, you can see why sometimes they are such a difficult opponent. The ability to remain in the cocoon for so long means that flea eggs laid in the summer can survive the winter and emerge in spring, leading to a sudden explosion of numbers in as short as a fortnight. This highlights the importance of using flea control all year round to keep the fleas in the environment under control.