Fleas are everywhere on every continent, but most people don’t really think much about them anymore. I mean, the Black Death was a long time ago, right? The facts are found everywhere, on every continent. The fleas in Antarctica feed on a variety of seabirds, but if there was a large population of dogs and cats there, I’m sure the cat flea would be there too. Fleas have been around longer than humans, their flea fossils embedded in amber dating back to the upper Eocene and Miocene periods.
There are over 2,000 flea species, but pet owners need to be concerned with just one: Ctenocephalides felis, the cat flea. This flea doesn’t just feed on cats. While it prefers blood from cats and dogs, it will feed on humans in a pinch. Interestingly, human blood isn’t nutritionally complete enough to allow much reproduction, which is why they prefer our furry friends. They have a wide host range, including raccoons, opossums, and birds, which is why eliminating fleas on pets that go outside can be difficult.
When I see a cat or dog for a wellness exam, I first comb them with a flea comb. Owners often say, “You shouldn’t find anything. I use a preventative on them.” But sometimes I do find a live flea or, more commonly, flea dirt. Because of flea preventative use, I’m more likely to find evidence of fleas in December and January—the months people decide it’s too cold for fleas and stop using a preventative.
Although the cat flea doesn’t transmit plague, which is spread by the rat flea ( Xenopsylla cheopis ), it causes other health problems. The most common allergy in dogs and cats is to the saliva from a flea. For affected pets, just one flea bite is enough to cause scratching and biting.
Cat scratch fever is another disease caused indirectly by fleas. The flea can be infected with Bartonella henselae, the bacteria causing cat scratch disease. A cat gets infected by the bacteria when bit by a flea or from fighting with an infected cat. Cats don’t usually show any clinical signs, but if an infected cat scratches, bites, or licks an open wound, you can get a nasty infection.
Mycoplasma is another bacterial infection transmitted to cats through flea bites, as well as by tick and mosquito bites. The bacteria infect the red blood cells, causing anemia and fever in cats. Because fleas can bite humans, Mycoplasma can infect people too.
Adult fleas are visible to the human eye, but are less than an eighth of an inch long. They have pretty flat bodies, no wings, and backward-pointing hairs, which make it easy for them to navigate between hairs on your pet. They also have strong hind legs, making them great jumpers, and a hard exoskeleton, so it’s difficult to squish them. When I catch one in my flea comb, I have to get it trapped and squished under my fingernail before it jumps away (they can jump up to 7 inches vertically or 13 inches horizontally). Interestingly, bat fleas don’t jump—they’re blind and live high up in the air, so jumping could plunge them to their death.
Both male and female fleas feed on blood, required to mate and reproduce. Males are half the size of females and don’t need as much blood. An unfed female flea will increase in weight 140 percent after feeding. That’s like a 125-pound woman gaining 175 pounds after eating dinner!
Both sexes take in more blood than they need, excreting the excess as feces, also known as flea dirt. If I find thin black bits on the flea comb, I put them on a damp, white paper towel. If they leave a rust spot, I know it’s dried blood from a flea. About 40 eggs are laid on a cat or dog per female flea per day. Then the eggs fall off as the pet moves, along with the nutrient-rich flea poop. Adults can live for up to a year in ideal conditions, which means if you see just one flea, you have a lot of eggs in the environment.
Eggs take anywhere from two days to two weeks to hatch, depending on humidity and heat in your house. Optimal conditions are 70 to 85 degrees Fahrenheit and 70 percent humidity. The emerging maggots (larvae) are tiny, white, and legless. They feed on flea dirt along with skin and hair from the pet. Maggots don’t like light, and hide under the pet’s bedding and carpets. Maggots will spin cocoons within 5 to 20 days of hatching and become pupae.
The cocoon protects the pupae for days to years, depending on the environment. This is why you might move into a house that has been empty for months and suddenly find fleas on your pets—the pupae didn’t hatch until they felt the vibration of your pet moving around. Cocoons are sticky, which makes it very difficult to suck them out of carpet or from the cracks between hardwood floor slats. The cocoon is also resistant to chemicals that might kill adult fleas. Once a flea hatches from the cocoon, it’s an adult and uses its powerful legs to jump onto a host, where it will stay for the rest of its life.
In the past, and even now, people would treat fleas on their pets with ineffective shampoos; dips; and smelly, dusty flea collars. These would help decrease the adult flea population for a short time, but 95 percent of the flea population in a house is not on the animal. Flea bombs or sprays can help, but they put a lot of chemicals in your environment. The good news is that there are very effective prescription products available to prevent flea infestations on your pets.
If your pet has fleas, plan on cleaning your house thoroughly each week for the next three months and treating your pet every 30 days with a veterinarian-approved preventative. Vacuum the house thoroughly and throw away the bag or clean out the canister. Wash all your bedding and things that your pets sleep on in hot water.
People are horrified to find their pets have fleas, but fleas are ubiquitous in the environment and not an indication of an unclean house. I recommend treating all pets year-round for fleas. Anyone can bring fleas in from outside, and it only takes one female flea on a pet to start a huge problem.
Lori Scarlett, DVM, is the owner and veterinarian at Four Lakes Veterinary Clinic. For more information, visit fourlakesvet.com .