Flea Identification: How to Tell Fleas From Look-Alikes

• Fleas have laterally flattened bodies and enlarged hind legs specialized for jumping and are strong jumpers, unlike bed bugs, which are flattened top-to-bottom and can only crawl.
• Adult cat fleas remain on the host (cat or dog) for feeding, mating, and egg-laying, and are commonly found on pets and where they rest, rather than leaving after biting.
• Flea larvae are slender, worm-like, and legless, completely different in form from adults, and are commonly found in pet bedding, carpets, or soil in areas animals frequent.
• Flea bites typically consist of a small, central red spot surrounded by a red halo, usually without significant swelling — a useful preliminary clue for identification.

People most often mix fleas up with:

• Bed Bugs
• Lice

Open the other page and compare its list against the marks above; the differences are usually in the antennae, wings or the way the body is divided.

Fleas bite pets and people, causing itching at the bite site; some people and pets develop allergic dermatitis from flea bites, with intense itching, hair loss, skin redness, and secondary infection. Fleas can transmit a murine typhus-like disease (cat flea rickettsiosis) and serve as an intermediate host for cat and dog tapeworms. Seek medical care promptly for severe symptoms or any allergic reaction.

The source describes fleas as a pest that troubles people and pets, with numbers increasing markedly in spring and early summer; no beneficial role is mentioned.

Mainly live on pets (cats and dogs), and in carpets and resting areas pets frequent; larvae are found in animal nests or soil in areas animals frequent.

Get as close as your camera will focus, from directly above, in daylight or a bright lamp. Include the whole body with the legs and antennae in frame; a second shot from the side shows wings and body segments. Put a coin or ruler next to it for scale. For a bite or a bug found on skin or bedding, photograph the bug itself, not the mark. The app names the likely group; use the list above to confirm.

You can tell a flea from other tiny dark bugs with five checks:

• Size: 1/16 to 1/8 inch (University of Maryland Extension); Ohio State gives about 1/8 inch for adults.
• Colour: dark reddish-brown to brownish-black (Ohio State; UMD).
• Shape: flattened from side to side, so it looks thin from above and tall from the side (Ohio State).
• Wings: none.
• Movement: strong jumps, using enlarged hind legs.

Under magnification, the cat flea (Ctenocephalides felis) has comb-like rows of spines on the cheek (genal comb) and behind the head (pronotal comb), and a longer head than the dog flea (Wikipedia). The cat flea is the one found on most dogs and cats: UC IPM notes the dog flea is rare in California. For species-level work, the Orange County Mosquito and Vector Control District publishes a pictorial flea key and a guide to mounting fleas for a microscope.

Most of a flea problem is not on the pet. Ohio State says a female can lay 15 to 20 eggs a day, up to 600 in her lifetime; eggs hatch in about 2 to 14 days, and the whole cycle takes from two weeks to eight months.

• Larvae: up to 3/16 inch, hairy and wormlike, with a brownish head and no eyes or legs (UC IPM); UMD describes them as whitish and about 1/5 inch when mature. They live in carpet, cracks in wood floors and pet bedding, and eat the dried blood that adult fleas pass.
• Pupae: inside a cocoon in the carpet. At cool temperatures a fully formed flea can wait inside for up to 12 months; warmth and the pressure of footsteps or vacuuming trigger it to emerge (UC IPM).

That waiting stage is why new fleas keep appearing for weeks after treatment, and why flea larvae in carpet are sometimes mistaken for other small household larvae; see larvae identification.

Adult fleas pass excess blood as small black pellets that fall off the pet (Ohio State). Comb your pet or brush bedding onto a damp white paper towel: Ohio State says the pellets turn the water bright red when moistened. Plain dirt stays brown or black. Check the neck, shoulder blades and base of the tail, where Ohio State says fleas concentrate.

A second test from UC IPM: walk around the pet's resting areas wearing white socks pulled up to the knee. If fleas are present, they jump onto the socks, where they are easy to see.

• Springtails: 1/8 inch or less, grey to white, and they jump, but they live in bathrooms, around flower pots and in damp areas, not on pets (University of Maryland Extension).
• Bed bugs: flattened top to bottom, not side to side, 1/4 to 3/8 inch, and they crawl rather than jump (UMD). See bed bugs.
• Bird mites: very tiny, they bite, and they come in through windows and vents (UMD).
• Lice: see lice for how they differ.

If it jumps and you have pets, it is most likely a flea. If it jumps and you find it by the sink or a houseplant, it is more likely a springtail.

• Itchy bites on the ankles and lower legs: Ohio State describes a small, hard, red, slightly raised spot with a red halo.
• Black specks on sheets or pet bedding that turn red on a damp tissue (the flea dirt test).
• A pet that sleeps on the bed scratching and biting at its legs, belly and back (Ohio State).
• Tiny dark insects that jump when you pull back the covers.

Fleas concentrate where pets sleep (UC IPM), so if a pet shares the bed, treat the pet and wash the bedding. For bite appearance and when to see a doctor, see flea bites.

Nothing clears a house instantly, because pupae in their cocoons are protected and can wait for months (UC IPM). What works is a routine that removes each stage, from UC IPM and Ohio State:

• Vacuum daily or every other day where pets rest; vacuuming also triggers pupae to emerge so the new adults can be removed.
• Wash pet bedding in hot, soapy water at least once a week.
• Treat every pet with a flea product recommended by your veterinarian.
• Treat the heaviest areas with a product containing an insect growth regulator such as methoprene or pyriproxyfen, which UC IPM lists for indoor use, following the label.
• Call a professional for severe infestations (Ohio State).

Expect to keep going for several weeks. Adult fleas survive about a week without a blood meal but can last from two months to several years between meals (Ohio State).