Fleas are, by far, the most common external parasite of pets, making flea allergy dermatitis the most common skin disease of cats and dogs. The most common species of flea found on our pets is Ctenocephalides felis. The most successful way to control fleas is to disrupt their life cycle. That means that owners must treat both their pets and the environment (house, yard, etc). Adult fleas live on your pet, where they eat and reproduce. The fleas seen on our pets make up only about 5% of the total flea population...the other 95% is found in the environment. Flea eggs, in general, fall off the host shortly after they are laid. Once the eggs hatch, the larvae develop, feeding on digested blood (poop) that has fallen from the host from the adult fleas. The larvae grow, finally making cocoons (pupae). The pupae can remain dormant for months, and emerge when suitable conditions are present. Vibrations, warming, and increased carbon dioxide can all signal to the pupae that a suitable host is present for them to inhabit. This entire life cycle can take as few as 16 days. The best control methods are treating pets to prevent them from bringing fleas into their environment and to treat the environment. Many products are available and include monthly topicals, pills, and sprays.
In addition to the itching fleas can cause pets (and even you), fleas can also lead to anemia in animals (especially in young puppies and kittens), tapeworms (from ingesting fleas), and diseases like plague (that last one is pretty rare around here, but it is a disease that can also occur in people).
Ticks are another pesky little parasite, but, unlike the other pests on this post, they are not insects. Ticks can act as vectors to transmit many diseases that people and animals can both acquire. A couple of examples are Lyme disease and Rocky Mountain Spotted Fever. They can also cause a syndrome known as tick paralysis, in which the nervous system is affected by the presence of a tick. Ticks can be controlled by various products, including monthly topicals, sprays, and PrevenTic collars, among others.
Biting flies tend to like chewing on dogs' ears and open wounds. They can be controlled with creams that can be applied to the pets' ears, some monthly topicals, and sprays.
And, finally, we reach the mosquito. Aside from being a nuisance by biting and making us itch, mosquitoes can cause a wide variety of conditions. Around here, in the Mississippi Delta, the biggest condition they lead to is heartworm disease. Recommendations for controlling these giant six-legged monsters include leaving no standing water for the mosquitoes to lay their eggs. Many cities have trucks (or small planes) that release chemicals meant to kill the mosquitoes. Some monthly topicals and sprays are labelled to repel mosquitoes, but, at least around here, there doesn't seem to be much that makes a dent in their population. It is critically important that pets remain on heartworm preventatives year-round.