Fleas are insects and belong to the order Siphonaptera which means "wingless siphon," an apt description of the ravenous blood sucking parasites. There are over 2,000 species of fleas worldwide. The different species of fleas prefer to live separately and do not interbreed. More than 99% of flea infestations in domestic pets are due to the cat flea, Ctenocephalides felis.
Fleas are important because of their harmful effects on animals (and people) and the diseases they can transmit. The rat flea,* Xenopsylla cheopis*, 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. The tropical hen flea or the sticktight flea is also known as* Echidnophaga gallinacea.* 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 cats. 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.
Flea Anatomy
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. The last pair is greatly enlarged, which equips them with their incredible jumping ability. Fleas have no wings; therefore, fleas are unable to fly. 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 even survive several months without taking a blood meal.
The Flea Life Cycle
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, the eggs 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, 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.
Two days (or more depending on temperature) after the egg is laid, it hatches. The larva emerges, which looks like a small maggot, and it starts to feed on the feces left by its mother. The larva passes through several phases of development over 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.
Problems Caused by Fleas
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.
Large numbers of fleas can cause anemia, especially in puppies and kittens, due to excessive blood loss. Some pets have been known to die if the anemia is severe.
Diagnosing Fleas
The diagnosis of a flea infestation can be made by finding the adult fleas or flea dirt on the animal. Flea dirt looks like little black flecks on the pet's skin. The best places to use a flea comb to detect fleas is around the hindquarters and head of the pet. These same areas should be examined for the flea dirt. After using the flea comb, transfer any debris found on the comb to a piece of white paper toweling and moisten it. If the dirt dissolves into a red color, it is flea dirt.
Diseases Transmitted by Fleas
Fleas can transmit several different diseases and even other parasites. Many pets become infected with a tapeworm called* Dipylidium caninum* caused by ingesting an infected flea. Haemobartonellosis, also known as Hemotropic mycoplasmosis, which affects red blood cells. Another parasite called Dipetalonema reconditum is found in the bloodstream and is transmitted by fleas. Luckily, Dipetalonema does not require treatment. Plague is caused by the bacteria Yersinia pestis, also transmitted by fleas. Typhus, caused by Rickettsia typhi, is an infectious disease characterized by rash, headache, fever, and may even cause delirium. Tularemia, or rabbit fever, is caused by Francisella tularensis. Tularemia is a bacterial infection characterized by ulcers, fever, and weight loss. Humans are also at risk of contracting tularemia.
See our article on Flea Control for more information on how to prevent fleas and flea-transmitted diseases in dogs.
Article by: Race Foster, DVM and Angela Walter, DVM