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By Kate Hughes

Most pet owners have some experience dealing with fleas. After all, fleas are indiscriminate parasites, happy enough to feed off of dogs and cats, ferrets and rabbits, and, of course, humans, when the need arises. While a lot people have encountered these nasty little parasites, they know very little about them. However, despite being quite troublesome for pet owners and their furry friends, fleas are actually interesting creatures. So read on to learn more about them. As you go, it’s natural to feel a little itchy—but try not to scratch!

1. Fleas have a flexible life cycle. A flea’s life cycle can be broken down into four parts: egg, larva, pupa, and adult. The adult lays eggs on a host, which then roll off into the environment. When these eggs hatch into larvae, the larvae hunker down in the environment, feed, and go through several molts until they spin a cocoon and become pupae. Eventually, from the pupae emerge adult fleas, which then seek out an animal host for a blood meal. Under ideal conditions, this entire process takes about 21 days. However, fleas have a very flexible life cycle, and will wait until conditions are optimal to move from one stage to another. “The more warm and the more moist it is, the faster the life cycle will go,” says Dr. Ann Hohenhaus, a staff doctor at NYC’s Animal Medical Center, who specializes in small animal internal medicine and oncology. “If it’s cooler and dryer, the process slows down until the temperature goes up.” 

2. While neat, this life cycle makes fleas insanely hard to eradicate. Fleas are hardy creatures. Dr. Daniel Morris, a professor of dermatology at the University of Pennsylvania School of Veterinary Medicine in Philadelphia, says that most of the flea medications on the market will kill adult fleas, but it’s much more difficult to be rid of eggs and especially pupae. “Some products have a compound that keeps eggs from hatching, but don’t kill the pupae,” he says. This means that even if you wipe out all of the adult fleas in an infestation, the next generation might just be waiting to take up the reins.

3. During a flea infestation, treating your pet isn’t enough. You have to treat the environment too—that’s where the eggs and pupae are hiding. “I always tell my clients that killing the fleas on their pets isn’t enough. There are eggs and pupae in the carpet, in between the floor boards, and even in your car, if you have a habit of taking your dog on rides,” Morris says. Hohenhaus adds that if you vacuum during a flea infestation, you should immediately throw that vacuum bag out because any eggs and pupae you vacuum up may still be viable. “You also want to wash everything—bedding, clothes, etc.—in hot water,” she says. In the case of a particularly bad infestation, both Morris and Hohenhaus recommend enlisting the services of an exterminator. 

4. Fleas can go a long time without eating. Research shows that pupae can stay in their cocoons for up to a year. Once the adults emerge, they try to find a blood meal immediately but, if necessary, can survive for one to two weeks without eating. However, it is only after they eat that they can lay eggs. They’re also indiscriminate feeders. “If you go away for a weekend and don't realize there are fleas in your house, the moment you walk on the carpet in your living room, you've got flea bites up to your knees,” Hohenhaus says. “This is because the fleas are starving and they're looking for a blood meal.”

5. A female flea can lay up to 50 eggs per day. Typically, it’s more like 20 eggs, but that means that a single prolific female flea can cause a major infestation in less than two months. “If you start with one female flea at maximum egg production, and assuming that half of the eggs are breeding females, in just 60 days you could have more than 20,000 fleas on your hands,” Morris explains. “This is how a serious infestation can happen before you even realize there is an issue.”

6. Fleas have Olympic-caliber jumping skills. It’s generally recognized that fleas are some of the best jumpers in the world, able to jump more than 150 times their body length. This ability is a necessity for the fleas’ life cycles. “If fleas are unable to jump onto an animal, they’re not going to be able to feed and then they can’t reproduce,” Hohenhaus says.

7. Indoor-only pets are not safe from flea infestations. Fleas, in all of their stages, are easy to transport from place to place. This means that even if your animals never go outside, they are still susceptible to fleas. That said, some animals are more at risk than others. An indoor cat who lives in a high-rise apartment in a major city is less likely to pick up fleas than an indoor cat who lives in a house in the woods. Also, some parts of the country—think warm and moist again—are more infested with fleas than others.

8. Your pets can develop an allergy to flea bites. According to Morris, there are two types of itching associated with fleas. The first is mild itching associated with the creepy crawly feeling of a bug on your skin. The second is a much more intense itch, which occurs when an animal develops an allergy to the proteins in a flea’s saliva. “Once an animal is allergic, the itch becomes impossible to ignore,” he says. “It’s itchy times 100.” If animals with an allergy are left untreated, the bites can become infected and require extensive veterinary care.

9. Fleas can transmit diseases that impact humans. Fleas are carriers of all sorts of bacteria, including bacteria that can cause disease in people. One of the more prominent examples is Bartonella henselae, which is the bacteria responsible for cat scratch disease.

10. Fleas can also transmit parasites. Fleas can also carry parasites, which they then transmit to their hosts. Tapeworms are most commonly transmitted by fleas. “When dogs and cats groom fleas off their bodies, they often swallow them,” Morris says. “If the flea is carrying tapeworms, they’ll then be released into the dog or cat’s intestinal tract.”

11. Flea infestations can make animals very sick. In severe infestations, fleas can consume so much of a host’s blood that the host becomes very ill. Some animals develop iron deficiency anemia, and smaller animals could even require blood transfusions. “This mostly occurs in young puppies and kittens,” Hohenhaus says. “Fleas are very efficient and effective parasites.”

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