The dark speck that suddenly appears when you walk across the carpet, then disappears, is likely a flea. It’s a bloodsucker, reddish-brown, about one-eighth of an inch long. Using a magnifying glass, you’d see the flea’s body is flattened from side-to-side and it has long claws on its legs – both are adaptations for traveling between hair shafts. The flea also has spines on its mouth, legs and back to help prevent it from being groomed off.

Nevertheless, a dog will probably pick off many of the cat fleas it hosts. Cat fleas (Ctenocephalides felis) are more common on cats, dogs and humans than dog fleas (Ctenocephalides canis) and human fleas (Pulex irritans). Each has its preferred hosts. The human flea prefers the blood of humans and pigs. Cat and dog fleas prefer cats and dogs, though children can become infested when pets sleep or rest on the same bed. Cat and dog fleas also will infest certain types of wild carnivores, including opossums and raccoons, but not squirrels, rats or mice. While these two species do not carry human diseases, they can carry tapeworms (Dipylidium caninum) that infect dogs.

Other flea species occasionally encountered by humans include the oriental rat flea (Xenopsylla cheopis) and the northern rat flea (Nosopsyllus fasciatus). These fleas live on Norway rats and roof rats, and are capable of transmitting plague and murine typhus to humans.

Fleas are small insects that survive by feeding on animal or human blood. Their bites can cause discomfort, itchiness, and irritation. Sometimes, fleas can infect people or pets with the germs that cause flea-borne typhus, plague, or cat scratch disease.

We are most familiar with adult fleas, those specks that jump and occasionally bite, but spend most of their lives on cats and dogs. Fleas reproduce rapidly. Eggs are laid on the animal while it sleeps or rests. They are not sticky and fall down into the pet’s bed – where the offspring are most likely to find food.

The eggs hatch into tiny (1/8-inch) larvae; white, worm-like, legless and blind. They shy away from light and wiggle their way down into the animal’s bedding, carpet, grass, etc. This stage has chewing mouthparts and does not suck blood. They do, however, feed on digested blood in the form of feces from the adult fleas, as well as bits of dead skin, feathers and other organic debris. After growing through three molts (shedding of the exoskeleton) the larvae become pupae, spinning silken cocoons, which they camouflage by attaching bits of debris.

Perhaps a month after the eggs are laid, adult fleas emerge from their pupal cocoons. Emergence of adults is triggered by heat (of people and pets), carbon dioxide (breath) and by physical pressure (e.g., from people and pets walking or lying on them). Thus the movements of unsuspecting humans can attract newly-emerged cat fleas that would otherwise prefer cats and dogs. To improve chances of contacting a passing host, newly-emerged fleas tend to move upward on vegetation, carpet, drapes and furniture. Their eyes are most sensitive to yellow-green light – the color of vegetation – and they are attracted to dark moving objects against a light background, such as a dog against foliage, or a person against a wall. To contact a host, they jump a distance of up to one foot after detecting the presence of warmth and carbon dioxide. Once it makes contact, the cat flea begins feeding on the host’s blood. If dislodged, it usually dies within two days.

Fleas often probe the skin before taking a blood meal. After 30 minutes, lines or clusters of itchy red marks appear. On sensitive persons, bites develop into raised bumps within 24 hours after being bitten.

Fleas have been associated with humans and other animals for thousands of years. A bacterium (Yersinia pestis) spread by fleas killed 25 million people, more than a quarter of the European population, in 14 th century Europe. This was the “black plague.” Epidemics also occurred in Egypt, Africa, China, India and even the U.S., before the discovery of antibiotics. All told, perhaps 200 million people have died of plague – more than have died in all the wars in history.

Today, plague occurs worldwide. Each year, a few cases of bubonic plague are recorded in the United States, mostly in the Southwest. The disease is typically carried by wild rodents, and transmitted to the fleas that bite them. The digestive system of an infected flea can become blocked by rapid reproduction of the bacteria, causing the flea to bite repeatedly in an attempt to avoid starvation. Humans typically contract the disease from the bites of infected fleas, or through skin abrasions that contact the blood of infected animals or the feces of infected fleas.

Bubonic plague occurs most often where persons live or participate in outdoor activities in close proximity to wild rodents, such as rock squirrels, ground squirrels, prairie dogs, chipmunks and rats. Pets also bring plague-infected fleas into the home. Cats are highly susceptible to the disease. Outbreaks can arise in urban and rural areas, especially where conditions are primitive or unsanitary.

Symptoms of bubonic plague develop within one week of exposure to the bacterium, and may include headache, fever, weakness, fatigue and painful, swollen lymph nodes known as “buboes.” The disease responds well to antibiotics, but untreated persons may die within a week of showing symptoms.

Another disease transmitted by fleas is murine typhus. In the United States, only a few cases are reported annually. These typically occur in Texas, or result from travel abroad, especially to tropical countries. Transmission of a bacterium (Rickettsia typhi) that causes murine typhus takes place in rat-infested areas, in the same manner as mentioned above for bubonic plague, and by inhalation of airborne flea feces. Headache, body aches, fever and, occasionally, a rash and other symptoms develop within two weeks after infection. Like plague, murine typhus responds well to treatment with antibiotics.

There are more than 2,500 flea species worldwide, with more than 300 species occurring in the United States. However, of the many different fleas in the world, only a select few can affect people’s health.

Cat Flea (Ctenocephalides felis)

• Transmits: Flea-borne (murine) typhus and cat scratch disease (CSD)
• Comments: Despite the name “cat flea”, this flea is the most common flea found on pets (including dogs) and other domestic animals in the United States. It is capable of spreading plague bacteria, but does so inefficiently compared with ground squirrel or rat fleas.

Dog Flea (Ctenocephalides canis)

• Transmits: Aids in spreading Dipylidium caninum, a tapeworm commonly found in dogs and cats, but occasionally found in humans.
• Comments: Despite the name, the dog flea is not a common flea of the domestic dog in the United States.

Ground Squirrel Flea (Oropsylla montana)

• Transmits: Plague
• Comments: Frequently associated with ground squirrels, including California ground squirrels and rock squirrels, which are known to aid in the spread of plague bacteria to people in the United States.

Oriental Rat Flea (Xenopsylla cheopis)

• Transmits: Plague and flea-borne (murine) typhus
• Comments: A rat associated flea commonly known for transmitting plague bacteria globally.

In the United States, some fleas carry pathogens that can cause human disease, including:

• Plague — most commonly transmitted to humans in the United States by infected ground squirrel fleas, Oropsylla montana, and globally by infected Oriental rat fleas, Xenopsylla cheopis. Also, may be transmitted by improperly handling an animal infected with plague bacteria. Most U.S. cases occur in rural areas of the western United States.
• Flea-borne (murine) typhus — transmitted to people by infected cat fleas, Ctenocephalides felis, infected Oriental rat fleas, Xenospylla cheopis, or their feces (poop; also called “flea dirt”). Most cases in the United States are reported from California, Texas, and Hawaii.
• Cat scratch disease (CSD) — transmitted to humans most often after a scratch from a domestic or feral cat that has been infected by a Ctenocephalides felis flea, or through flea feces (poop; also called “flea dirt”) being inoculated through a cat scratch. CSD occurs wherever cats and fleas are found.
• Fleaborne parasites, such as tapeworms can spread to people and animals if they accidentally swallow an infected flea. Small children are at a higher risk than adults, as they may spend more time close to the floor and carpeted areas where fleas are found. Most infected people will not show symptoms and will not know they are carrying tapeworms.

How fleas survive

Most fleas have four life stages: egg, larva, pupa (in a cocoon), and adult.

This diagram shows the typical lifecycle of fleas. The lifecycle of fleas can be very quick or last many months to years depending on the environmental conditions throughout the life stages.

1. After finding an animal or human host and taking a blood meal, adult fleas will mate and begin laying eggs in the fur and surroundings of the host. Eggs will hatch in one to ten days depending on environmental conditions such as temperature and humidity.
2. After hatching from an egg, fleas enter their larval stage. Larvae are free moving and feed on blood and flea feces (poop; also called “flea dirt”), in order to continue their development.
3. Within 5-20 days of feeding on flea dirt, the larvae will spin a cocoon, and enter the pupa stage. The cocoon protects pupa from environmental conditions and insecticides/repellents for several days or weeks until adult fleas are ready to emerge.
4. Adult fleas will not emerge from the cocoon until there is a clear presence of a host, such as movement or body heat, which will signal that there is a blood meal readily available.
5. Adult females begin to feed from a host within a few hours of emerging from the cocoon and soon after will mate and begin laying eggs.

How fleas find their hosts

Fleas prefer animal hosts but will resort to biting people when animals are unavailable. Adult fleas find hosts by detecting body heat, movement, the vibrations caused by movement, and breathing.

How fleas spread disease

Fleas transmit germs that cause disease primarily through the processes of feeding on hosts or through fecal contamination, when infected flea feces (poop; also called “flea dirt”) are scratched into an open wound.

Dogs and cats are very susceptible to fleas, but they can be protected. To prevent fleas on your pet:

• Limit the amount of time your pet spends outdoors.
• Limit contact with wild and stray animals.
• Bathe and brush pets regularly.
• Check for fleas regularly.
• Fleas prefer warmer and more humid months, but if there is an animal to feed on, fleas can survive year-round.
• Talk to your veterinarian about flea control products that are right for your pet.
  • Treat pets for fleas year-round in order to kill adult fleas and prevent new ones from hatching.
  • Always follow product instructions.
• If you find a flea on your pet or in your home, learn how to get rid of fleas right away to avoid further infestation.

The best way to prevent fleas on people is to keep pets free of fleas. Most fleas in the United States prefer to feed on animals, however, people are sometimes bitten out of convenience when they share space or come into contact with a flea-infested animal.

To protect yourself from fleas:

• Use Environmental Protection Agency (EPA)-registered insect repellents containing DEET, picaridin, IR3535, Oil of Lemon Eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone. EPA’s helpful search tool can help you find the product that best suits your needs. Always follow product instructions. Do not use products containing OLE or PMD on children under 3 years old.
• Covering skin with long-sleeve clothing and pants will minimize exposure to bites. Flea bites often occur on the lower legs and feet, protect these areas with long socks and pants.
• Treat clothing and gear with products containing 0.5% permethrin. Permethrin can be used to treat boots, clothing and camping gear and remain protective through several washings. Alternatively, you can buy permethrin-treated clothing and gear.
• Do not feed or pet stray or wild animals.
• Always wear gloves if you are handling sick or dead animals.

It’s easier to keep fleas out of your home than it is to get rid of them. Fleas can live in carpets, bedding, and other surfaces in the home where pets frequent. To prevent an infestation:

• Sweep or vacuum well and often. Vacuum your carpets and rugs as well as cushions on chairs and sofas. Be sure to empty the vacuum bag outside when finished.
• Clean bedding, especially pet bedding, frequently with soap and water.

Fleas prefer habitats with shade, as they cannot tolerate the sun for long periods. To prevent flea infestations, make your yard as unattractive to fleas as possible by:

• Mowing frequently. Mowing exposes the soil to the sun, which fleas try to avoid.
• Avoiding over-watering. Fleas thrive in humid environments so keeping the yard dry makes it less inviting.
• Treating dog runs with insecticides to make it less prone to fleas.
• Raking thoroughly to remove any debris. This increases flea exposure to potential insecticides and removes any shaded and humid breeding places.
• Keep rodents and animals (e.g. opossums) away from your home:
  • Store food, including pet food, in tight sealing containers.
  • Remove brush, rock piles, junk, and cluttered firewood outside of your home.
  • Seal up holes in your home where rodents can enter.
  • Keep tight lids on compost and trash cans.

Additionally, wild and stray animals commonly carry fleas. Put away pet food to discourage stray animals from hanging around your home and limit your pet’s contact with wild and stray animals.

Getting rid of fleas is a difficult process due to the long lifecycle of a flea. Moderate to severe infestations will take months to control and require a four-step process for complete elimination:

1. Sanitation. Thoroughly clean areas where fleas frequently breed. This includes washing bedding, rugs, and pet bedding, and thoroughly vacuuming and sweeping floors and carpeted areas and along the edges of walls.
2. Pet treatment. Every pet in the home must be treated. Thoroughly bathe pets with soap and water, then comb them with a flea comb. Pay careful attention to face and neck regions, and the area in front of the tail. Soap will act as a gentle insecticide to kill adult fleas. Talk to your veterinarian about choosing the right flea control product for your pet.
3. Home treatment. Begin home treatment at the same time as pet treatment. This keeps all treatment on the same timeline and helps disrupt the flea life cycle. A licensed commercial pest control applicator can help you determine which products are best for inside your home and in the yard. In general, focus outdoor treatment on shady areas and places where pets spend the most amount of time.
4. Follow-up. Fleas have a complex life cycle. At some stages of their life cycle they are resistant to insecticides and other flea control products. In order to get rid of fleas in all stages of the life cycle, two or more follow-up treatments within 5-10 days after the first application are needed. Additionally, vacuuming and sanitation practices should be ongoing throughout this period to pick up all remaining eggs and juvenile fleas.