Bed Bug ID: Size, Life Stages, Signs and Look-Alikes

• Bed bugs are flattened top-to-bottom and oval, and adults are wingless for life, only able to crawl and not jump — clearly different from fleas, which are laterally flattened with hind legs specialized for jumping.
• Bed bugs are smaller, more rounded, and wingless as adults, distinguishing them from the larger but similar-looking kissing bug (conenose bug).
• Bed bugs hide by day in concealed spots such as mattress seams, bed frame joints, and behind loose wallpaper, coming out at night to feed on blood — you need to check these hiding places rather than only looking at the person's body.
• Bed bug bites are usually painless and go unnoticed during sleep, with redness and itching appearing only days later; but distinguishing the bite itself from mosquito, flea, or spider bites is difficult to impossible.

People most often mix bed bugs up with:

• Fleas

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.

Bed bugs feed on blood; bites are usually painless and hard to notice during sleep. Anticoagulant and anesthetic compounds in their saliva typically cause an allergic reaction — a colorless welt or bump at the bite site that turns red and itchy only days later — though some people have no reaction at all. The source explicitly states bed bugs do not transmit disease. Seek medical care promptly for severe symptoms or any allergic reaction.

Mainly hide in bedrooms: mattress seams and tufts, inside box springs, bed frame joints, behind headboards/footboards, under loose wallpaper — crevices close to the sleeping area.

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.

An adult bed bug is a flat, oval, wingless, reddish-brown insect about the size of an apple seed: 5 to 7 mm (3/16 to 1/4 inch) long, according to the US Environmental Protection Agency (EPA). After a blood meal it swells, turns redder and becomes longer; Cornell University's IPM program describes a fed bed bug as football-shaped.

• Eggs: pinhead-sized and pearl-white (EPA). Cornell gives about 1 mm and calls them bean-shaped and translucent white. EPA notes that eggs more than five days old show an eye spot.
• Nymphs: five stages before adulthood. EPA's life-stage chart runs from about 1.5 mm to 4.5 mm. Unfed nymphs are translucent or whitish-yellow and, EPA says, can be nearly invisible to the naked eye; Cornell notes a dark spot shows in the belly after feeding.
• Adults: UC IPM gives about 1/5 inch and Penn State Extension about 1/4 inch. Unfed adults are thin enough to slip into a crack the width of a credit card (Cornell).
• Pace of an infestation: UC IPM says the life cycle from egg to adult takes five weeks to four months, a female lays 200 to 500 eggs in her lifetime, and bed bugs can survive 20 to 400 days without feeding.

• Dark spots of dried excrement on mattress seams and the bed frame. Cornell notes they smear rusty-coloured when wiped with a wet tissue.
• Shed skins: tan skins left by growing nymphs (University of Kentucky).
• Eggs and empty eggshells in seams and cracks.
• Rusty or reddish smears on sheets from crushed, engorged bugs (University of Kentucky; CDC).
• A sweet, musty odour, which Penn State says indicates a moderate to high infestation.

Bites alone do not prove bed bugs. Penn State Extension says bites should never be used for diagnosis, and CDC notes bite marks can take up to 14 days to appear. Pair bites with at least one of the physical signs above, or have a specimen identified.

Penn State Extension lists ticks, fleas, cockroaches and carpet beetles as the insects most often mistaken for bed bugs, and UC IPM adds bat bugs, swallow bugs and conenose (kissing) bugs.

• Bat bugs and swallow bugs: close relatives that look almost the same. The difference is the hairs on the plate just behind the head: on a bed bug they are shorter than the width of the eye; on bat and swallow bugs they are longer (Cornell; UC IPM). You need a hand lens or microscope, so if bats or bird nests are near the bedroom, send a specimen to an extension office or pest professional.
• Carpet beetles: adults are round, 1/10 to 1/8 inch, with short antennae, solid black or mottled white, brown and yellow, and are usually found on window sills and drapes (UC IPM). Bed bugs are flat, oval and wingless, and stay near the bed.
• Conenose bugs: up to 3/4 inch, winged as adults and more pointed in shape (UC IPM), so far bigger than a bed bug.
• Ticks, fleas and cockroach nymphs: compare side by side with ticks, fleas and cockroaches.

Bed bugs live mostly in the mattress and the bed structure, not in the sheets. CDC lists the seams of mattresses, box springs, bed frames and headboards, dressers, cracks and crevices and the space behind wallpaper, and says they tend to stay within 8 feet of where people sleep. UC IPM names mattress seams and tufts and the wood joints of box springs; Penn State adds the inside of mattress coils. The University of Kentucky also lists the edge of wall-to-wall carpet, baseboards and the backs of pictures, outlets and switch plates.

The sheets and pillowcases are where you notice the evidence: small blood smears and dark spots. CDC notes that bed bugs can travel over 100 feet in a night, so check the whole bedroom, not only the bed.

Heat kills bed bugs fastest. Penn State Extension says temperatures of 131°F or above are lethal to all bed bug stages, and properly applied steam killed all life stages on mattress surfaces. For anything that can go in a dryer, the University of Kentucky says 10 to 20 minutes at medium to high heat kills all life stages. Whole-home heat treatment is a job for professionals: UC IPM gives at least 140°F for two hours or 130°F for three hours.

• Cold is slow. EPA says 0°F for three days in a sealed bag, and many home freezers are not cold enough, so check with a thermometer.
• Do not heat the house with a thermostat, space heater or fireplace. EPA says this does not work and is dangerous.
• Skip foggers (bug bombs). UC IPM says over-the-counter total-release foggers have been shown to be ineffective against bed bugs and potentially harmful to residents; EPA warns that misuse can cause a fire or explosion.
• Expect resistance. UC IPM notes that insecticide resistance is increasingly common and the most effective products are available only to commercial applicators, so a confirmed infestation usually needs a professional.

CDC says bite marks appear on the face, neck, arms, hands or any other part of the body left uncovered during sleep. Reactions range from none at all to itchy welts (Cornell), and bed bugs are not known to spread disease to people (CDC). For what the bites look like and how long they take to appear, see bed bug bites. See a doctor for a bite with spreading redness, fever or any strong allergic reaction.