Adult Fleas

picture of an adult cat flea on a white backgorund

Tom Murray

Img 1 Profile picture of an adult cat flea. View more pictures.

laterally compressed cat flea picture


Img 2 Top-down picture of an adult flea. View more pictures.

This page provides a quick summary of adult fleas, in the form of a FAQ. Click on the answers for detailed information, including citations.

What do adult fleas look like?
Adult fleas are 1.5 to 3.2 mm long. Females are larger than males. Like all insects, fleas have 6 legs and 3 primary segments (head, thorax, abdomen). Their dark brown bodies are flattened from side-to-side to allow for easy movement through host hair Img 2. The legs are long and specialized for jumping. Bristles, spines, and combs cover the body.

Do fleas have wings?
No. Fleas don’t have wings and can’t fly.

Do fleas have eyes?
Yes. But they don’t have compound eyes like most insects. Instead, they possess simple black eye-spots, which serve as light sensors.

Do fleas have antennae?
Yes. But the antennae are tiny and hidden in grooves. They can’t be readily seen.

Do adult fleas shed?
No. Only the larval and pupal stages shed their cuticle to allow for growth. Adults stay the same size, aside from abdomen expansion during the first feeding.

How far and high can fleas jump?
The average jump distance is 8 inches. The average height is 5.2 inches.

Can fleas walk and run?
Yes. Crawling is their primary mode of locomotion. Jumps are only performed to acquire a host. Once on a host, the fleas stay there. They’re specially adapted for moving through host hair.

How long do adult fleas live?
Fleas live for around a week on hosts. Host grooming is the primary mortality factor. If animals are restricted from grooming, the fleas can live for up to 185 days.

At what temperature do fleas die?
Adult fleas can only survive between 46.4°F and 95°F (8°C and 35°C). However, they can survive winters on their warm-bodied hosts.

How long can fleas live without host blood?
Fleas removed from their host will starve within 4 days. Unfed fleas can survive slightly longer without a blood meal. Adults within their cocoons can survive for up to 155 days.

How many fleas can live on animals?
Usually dogs and cats will have less than 20 adult fleas on them. However, in severe cases, on-host populations can exceed 300.

Where do adult fleas live?
Adult fleas emerge from cocoons in the environment (carpets). However, once they jump onto a host, they’ll stay on the animal.

Do fleas stay on humans?
No. Humans aren’t the preferred host of fleas, partly due to our lack of body hair. When fleas bite people, they take a blood meal and then leave.

Can fleas survive and reproduce on human blood?
Not in normal settings. They must feed freely for many hours, which doesn’t happen outside of laboratory settings. Even with sufficient feeding, their reproductive capacity is drastically reduced on human blood.

Do fleas sleep?
Insects don’t sleep. But fleas do have cycles of rest and activity. They’re most active at sunset, and least active at sunrise.

Do fleas drown in water?
Fleas don’t drown easily. It takes at least 24 hours for them to die when submerged. Adding dish soap to water causes them to sink and drown faster. This is due to the surfactant properties which reduce water’s surface tension.

Can fleas swim?
No. But they also don’t sink. They’ll fail around on the water’s surface trying to escape.

What attracts fleas?
The primary attraction stimuli are visual and thermal cues. Other stimuli help to reinforce host detection.

Are fleas attracted to white?
White is the least attractive color to fleas. But they are easiest to see against white surfaces.

Are fleas attracted to water?
No. Homemade flea traps use water to drown fleas, but a light is used to attracted them.

Can fleas see?
Yes. But their simple eyes serve only as light sensors. They can’t form acute visual images. They can detect wavelengths between 300 and 600 nanometers, being most sensitive to green-yellow light (515 nm).

What is flea dirt?
Flea dirt is the feces from adult fleas, composed largely of undigested host blood. It’s excreted onto the host, and dries into black-red specks. When the animal grooms itself, the flea dirt falls into the environment to feed larvae.

Do fleas have blood in them?
Insect “blood” is called hemolymph. However, after feeding, adult fleas can hold around 5 µl of host blood in their abdomens.

How do fleas mate?
Fleas find mates and copulate on their host. Mating begins around 24 hours after the first blood meal. Females must mate with multiple male partners to reach maximum fertility.

What percent of infestations are adults?
Adults make up 1-5% of flea infestations. For every adult, there are around 100 immature stages living in the environment.

What’s the best way to kill adult fleas?
Please see our page on How to get rid of fleas for control information. Effective techniques to kill adults include vacuuming, laundering, and using modern adulticides.

Please leave a comment below if you have any questions that weren’t addressed, and I’ll add them to the list.

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