Fleas: Life Cycle, Anatomy & Disease Transmission
Drs. Foster & Smith Educational Staff
Fleas are insects and thus belong to the order Siphonaptera which means 'wingless siphon,' an apt description. Worldwide,
there are over 2,000 species of fleas. They prefer to live separately and do not interbreed. Fleas are important because of their
direct effects on animals (and people) and because of the diseases they can transmit. Some of the more important fleas
Xenopsylla cheopis is commonly known as the rat flea and is the carrier of bubonic plague. Known as the 'Black Death' in the
Middle Ages, bubonic plague killed 200 million people. The name "rat flea" implies that rats are the preferred host, but the
flea also lives on people, dogs, and cats.
Echidnophaga gallinacea is also known as the Tropical hen flea or the sticktight flea. It is mainly a flea of birds, but will also
feed on other animals.
Pulex irritans is the human flea. This flea also infests swine, and occasionally dogs and cats.
Ctenocephalides felis is the domestic cat flea, but it actually prefers dogs. This is the most common flea that affects dogs and
Ctenocephalides canis is the common dog flea. Despite its name, it also feeds on humans, cats, and other animals.
All of these fleas have their preferred hosts, but all will feed on dogs and cats. With such a huge range of fleas that can and do
feed on dogs and cats, it is easy to understand why their numbers are so difficult to control.
Fleas are insects, 2-8 mm long, and their body is divided into three parts: the head, thorax,
and abdomen. Attached to the thorax are three pairs of legs for a total of six. The last pair
is greatly enlarged, which equips them with their fantastic jumping ability. Fleas have no
wings. The most noted flea characteristics are their medium brown to mahogany color
and laterally flattened body. They are slightly smaller than a sesame seed.
Fleas have eyes and antennae, which detect heat, vibration, carbon dioxide, shadows, and changes in air currents, all of which
indicate a possible meal is nearby.
What do fleas eat?
Fleas, both male and female, feed on the blood of animals. They can go several months without a meal.
What is the life cycle of fleas?
There are four stages in the development of fleas: eggs, larvae, pupae, and adults. Male and female
fleas mate and two days later the female flea starts laying eggs. The eggs are often laid on the
animal, but because they are not sticky, fall off into the environment. Along with the eggs, the
female flea deposits a large amount of feces (often called 'flea dirt'). The feces, or flea dirt will
dissolve into a red color when moistened; this is because it is primarily digested blood. The flea
can lay 30-50 eggs in a day, generally in batches of 3 to 15, though she will not lay eggs every day.
A flea can produce 400-1,000 eggs in her lifetime (several months to two years, depending on the
Two days (or more depending on temperature) after the egg is
laid it hatches and the larva, which looks like a small maggot,
starts to feed on the feces left by its mother. The larva passes
through several phases of development taking a total of about a
week. At that time, the larva starts spinning a cocoon and is
called a pupa. The cocoon is sticky and will often become
covered with fine dirt or sand, and can be found deep in carpet
or crevices. In a week, the pupa develops into an adult and
emerges from the cocoon when it senses vibrations, carbon dioxide, or warmth, which tell it an animal host is near. The entire
life cycle takes about 15 days, but the pupa can remain dormant under inhospitable conditions (e.g.; cold) and extend the
cycle to over a year. This is important to remember when planning flea control.
What symptoms are caused by fleas and how is a flea infestation diagnosed?
Flea bites themselves may be unnoticeable on some pets, cause slight irritation in others, and
produce severe itching, red lesions, hair loss, and even ulcers in a third group. The severe lesions
are caused by a hypersensitivity to the flea saliva and is called flea allergy dermatitis.
In just thirty days, 25
adult female fleas can
multiply to as many as
a quarter of a million
Fleas can transmit tapeworms to your pet, as well as cause intense itching and allergic dermatitis. If you have an existing infestation, it is extremely important that you treat your home. We recommend professional house treatment, as there is much resistance to over-the-counter premise treatments. Please call our office for recommendations on treating/preventing flea infestation on your pet(s).