An Overview of the Life Cycle of a Flea

In the United States, more often than not, cat fleas (Ctenocephalides felis) are responsible for flea infestation in both cats and dogs.

Fleas are external parasites, that have tube-like mouth parts. These wingless insects pierce the skin of warm-blooded animals, including human beings, inject saliva to prevent blood clotting, and suck blood of the host. Injection of saliva causes an allergic reaction. A red welt that develops at the site of the bite becomes itchy and irritating.

Moreover, flea bites can result in an infection, as they can carry and transfer viruses, bacteria, and parasites, just like tapeworms. The bites are annoying, and lead to frequent scratching and biting by the animal. This can eventually result in hair loss, and anemia in extreme cases.

Pets like dogs and cats are their favorite hosts. Apart from animal skin, they are often found in basements, carpet fibers, gardens, yards, floor cracks, etc. They can be found on humans, cats, dogs, birds, chickens, rabbits, squirrels, rats, ferrets, etc. There are various species of fleas, out of which cat, dog, and rat fleas are the most common.

Holometabolism or complete metamorphism is the process that involves the four developmental stages. Insects belonging to the superorder Endopterygota go through these stages.

The life cycle length may vary from two weeks to several months, as it depends on the environmental temperature and humidity levels. Temperatures between 70 - 85°F and 70 - 80% humidity (hot and damp conditions) are the most favorable conditions for the flea population to flourish.

After sucking the blood of a host, an adult female lays small white, roundish eggs on the host itself. The eggs spread easily in the areas where the pet rests, sleeps, or plays. As they are not sticky, they easily slide off the pet's body. Thus, they get transferred to the carpets and bedding.

The eggs hatch within 2 (in warm and moist environment) to 15 (in cold and dry conditions) days. A hard spine at the top of the head helps the larva come out of the egg. The spine disappears as the flea attains maturity.

Larvae are white and semi-transparent. The average length of a larva is about ¼" or 6.35 mm. The body is covered with hair. They move around freely, and feed on available organic debris such as dead insects, feces, skin cells, pre-digested blood passed by adult fleas, and vegetable matter.

Some larvae follow a blood-only diet, while most follow a diet which includes blood, yeast, and other organic material. As they are blind, they try to avoid sunlight. This is why they can be found deep inside carpet fiber, or in dark places like bedding, floor cracks, etc.

The larval stage lasts for about 5 to 20 days. If the conditions are favorable, larvae start spinning silk cocoons within a week or two.

As the larva spins a cocoon around itself, it pupates. The pieces of dirt and debris it collects help build a cocoon, which works as camouflage. The cocoon protects the pupa from chemicals. It has a sticky outer covering, with the help of which it keeps itself attached to the surface of a carpet or bedding. Light sweeping doesn't remove these pupae.

If they get ample food, adult fleas emerge after about a week. They can emerge even within 3 to 5 days, or they can rest in the cocoon for a year or more. A flea comes out of the cocoon only when a host is present in the nearby area. It receives a signal when a host (for example, a pet) passes by.

The sound, vibrations, heat, and carbon dioxide emitted by a passing animal work as stimuli. These signals help the flea to know that a host is present, and that it is the right time to come out.

In suitable environmental conditions, an adult flea might live a year and a half, provided it gets ample food. Usually, it lives for 2 - 3 months. As the flea sucks the blood of the host, it becomes larger and lighter in color. It cannot live without a host.

If there is no food, it dies within a couple of days. Usually, the females are larger than the males. Each day, a flea consumes blood, which can even be 15 times its own weight.

Egg, larva, pupa, and imago (adult) are the four stages of a flea's life cycle. To get rid of fleas, you need to destroy the eggs, larvae, and pupae too. Flea population consists of about 50% eggs, 35% larvae, 10% pupae, and 5% adults. So, killing the adults cannot help eradicate fleas from a home. An adult flea can lay about 50 eggs at a time.

So, only two females can lay hundreds of eggs within a couple of days! As an adult female starts sucking blood, it becomes capable of reproduction. After emerging from the cocoon, if a female is not able to find food, it dies without reproducing. It lays eggs within 2 days of its first blood meal, and it can lay thousands of eggs during its lifetime.

Fleas don't have wings, but they can jump. They have long legs. With a strong pair of hind legs, they can jump vertically up to 7 inches (18 cm), and horizontally up to 13 inches (33 cm)! They don't have exceptionally strong muscles. With the help of energy stored in the form of resilin―the elastomeric protein―they jump and exhibit a spring-like action.

Fleas are dark-colored insects that have hard and polished bodies. Their bodies are covered with hair and short spines which are directed backwards. The laterally compressed bodies promote easy movement through hair, feathers, or clothing of their hosts. All these features help them survive strong attempts made by their predators to kill them.

Constant scratching by animals cannot do any harm to them. They are not easily killed by mashing or pressing either. Even squeezing between the fingers is of no use. Their bodies are so tough that they can easily withstand high pressures. One may have to roll them back and forth 10 - 15 times to disable their legs, and kill them.

To get rid of fleas, one can use insecticides, sprays, shampoos, dips, or apply medications topically. Some insecticides are capable of killing adult fleas only.

As mentioned earlier, adult fleas comprise only 5% of the total flea population, so one needs to kill the eggs, larvae, and pupae too, along with adult fleas. Consult a vet for the use of effective chemicals, and clean all the areas where a pet sits or sleeps (for example, car, bed, sofa, yard, etc.).