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Encyclopedia on Pets

This archive article (written 2009–2016) contains advice that may be out of date and is waiting for veterinary review. Please check with your vet before acting on it. About our articles

The Mighty Flea
Beware:

Though a flea is puny, its effects on pets and people can be mighty. Learn more about their bad habits and health consequences--and why you should talk to your veterinarian about keeping your pet flea-free all year long.

Fleas are one of the most troublesome problems that can afflict pets and the people who own them. However, they are also one of the easiest to prevent if you just take a few simple precautions.

Despite their tiny size, fleas can inflict outsize misery on pets. The continual itching and scratching that fleas can cause can make our animals miserable, especially as the weather grows warmer and fleas become more common.

In some unfortunate animals, fleas can also set off an extreme allergic reaction that can cause hair loss and skin lesions. These kinds of severe dermatologic problems can be difficult and costly to treat. In some rare cases, they can even be life-threatening. The bite of just a single flea can cause this kind of reaction in some highly allergic pets.

As if that isn’t bad enough, fleas can also transmit some nasty infections, such as tapeworm, to pets and people. In rare cases, they can play a role in the transmission of an unpleasant disease, called cat scratch fever, between humans and cats.

And in severe infestations, especially in old, ill, or young animals, feeding fleas can remove so much blood from a pet that they can cause debilitating anemia.

The Circle of Life
Over the years, fleas, like many other insects, have developed a remarkable life cycle that allows them to adapt and survive even under unfavorable conditions. While fleas are generally intolerant of the cold, certain stages of their life cycle have features that help them deal with that weakness.

Keep in mind, too, that our modern lifestyle is relatively flea friendly. We and our pets now live indoors in warm houses all through the winter, and that means that fleas are enjoying the good life along with us, too. For example, flea larvae often burrow into crevices, bedding, or rugs in the house, where they spin a cocoon and wait in the pupil stage until conditions are just right for them to emerge as adults.

Under ideal conditions, that can happen in as little as two weeks. Otherwise, they can exist in a sort of suspended state for weeks or even months. Once they are stimulated, however, by the right combination of heat, humidity, detectable movement, or the presence of a warm body, they emerge, eager to hop onto your pet and begin feasting and laying eggs.
Adult fleas, on the other hand, are able to over winter on our pets or on the local wildlife that is likely to be living in suburban backyards. These characteristics account for why flea infestations are a year-round problem throughout most of the United States, as well as for why they can be so difficult to get rid of once an infestation has taken hold.

Signs of Fleas
Surprisingly, fleas can be hard to detect. As a result, many owners don’t realize that their pets even have a flea problem.

In severe cases, an animal’s misery and skin irritations will make the presence of fleas more obvious. In mild infestations, however, it can be easy to be misled into thinking that your pet’s scratching or licking is just part of its normal grooming. This can be particularly true with cats, who like to groom themselves frequently. Here are some hints on how you can tell the difference:

First, carefully look for adult fleas behind your pet’s ears, around its head and neck, at the base of its tail, and in its "armpits" and "leg pits." You will sometimes see small, dark fleas scurrying around beneath the hair coat. (If your pet gets upset by your searching, have your veterinarian do this). Don’t be misled if you don’t see any fleas, however, because they are very good at hiding in fur and skin folds.

Next, you can check your pet for "flea dirt." Your veterinarian can do this during an exam, or you can do it yourself by running a special flea comb (you can get these at pet-supply stores) through your pet’s hair coat in some of the above-mentioned locations.

Periodically dump any loose hair or litter you collect in the comb on a piece of white paper towel. When you’re done, sprinkle a few drops of water on the debris. If any small, dark specks leave rust- or red-colored stains on the white towel — tada! — you’ve found flea dirt.
This is actually flea feces, and it’s composed of the leftover, dried portion of the blood meal that the fleas have taken from your pet. The flea dirt that falls off of your dog or cat then becomes the food that feeds the flea larvae that are developing in your pet’s bedding or environment.

Even if you don’t find obvious fleas or flea dirt, keep in mind that these pests may still be present. Cats, in particular, are very good at grooming fleas off of themselves. In some early infestations, your pet also may be scratching long before you see any signs of fleas. Flea infestations usually build over time.
Prevention Is Key