What do bed bugs look like?

You woke up with a line of marks on your forearm, you have been reading about it for forty minutes, and now every dark speck on the sheet looks like something. That is where most people are standing when they search this.

So here is the picture, at every size it comes in, and then the six other insects that get mistaken for it.

What an adult bed bug looks like: an apple seed that walks

The EPA describes an adult bed bug as about the size of an apple seed, 5 to 7 mm, long and brown, with a flat oval body when it has not fed recently. Texas A&M's Urban and Structural Entomology Program puts the same insect at about 1/4 inch, reddish brown, with an oval flattened body. The University of Kentucky adds a comparison that lands better for most people: the shape is like an apple seed, but the size is closer to a lentil.

Four things separate it from almost everything else you will find in a bedroom.

• It is flat. Not flat like a beetle, flat like a sheet of paper standing on edge. That shape is why it fits in a mattress seam and behind a headboard screw.
• It has no wings. There are small wing pads behind the head and nothing else. The University of Kentucky is blunt about it: bed bugs do not fly, or jump like fleas, but they crawl quickly over floors, walls and ceilings.
• It is one plain color. Brown, going redder after a meal. No spots, no bands, no pattern.
• It is covered in short golden hairs. You need a phone camera zoomed in to see them, but the EPA lists them, and they are the reason a bed bug looks slightly fuzzy at high magnification rather than shiny.

What it looks like after it feeds

Different insect, same bug. The EPA describes a recently fed adult as balloon-like, reddish brown, and more elongated. Texas A&M's own bed bug page leads with a photo captioned simply that human bed bugs change shape and color as they feed.

This is the single most common reason people decide they have two different pests. The hungry one is a flat brown disc. The fed one is a plump, dark red, stretched oval that looks swollen enough to pop. They are the same species, often the same night.

It matters for a practical reason too. A fed bug is no longer flat, so it cannot get back into the tightest cracks, and it will often shelter somewhere slightly more open. That is frequently the one you actually see.

At rest. Flat and compact.

Mid-meal. Swollen and stretched.

Bed bug nymphs and eggs, which is what you will actually miss

A bed bug grows through five nymph stages, and it needs a blood meal before each molt. The EPA publishes the size of every one of them, which makes this the rare pest question with an exact answer.

Bed bug size, egg to adult

Millimeters. The first three stages are smaller than a grain of salt.

EggPearl white

1

1st stage nymphNearly transparent

1.5

2nd stageWhitish yellow

2

3rd stageStarting to darken

2.5

4th stageTan

3

5th stageLight brown

4.5

AdultReddish brown

5-7

03.57 mm

The EPA says young nymphs are translucent or whitish yellow, and can be nearly invisible to the naked eye. That is the honest reason a self-inspection comes back clean and the problem does not go away. You were looking for a brown apple seed. What was there was a clear speck the width of a pencil line.

Eggs are about 1 mm, pearl white, and sticky when they are laid, so they sit glued into seams and screw holes rather than loose. The EPA notes that an egg more than five days old has a visible eye spot. Texas A&M records a female laying around 200 eggs in her lifetime, at three or four a day, hatching in 6 to 17 days.

A nymph. Clear, except for the meal.

Eggs, glued into a screw hole.

What they leave behind, which you will see first

Almost nobody finds the insect first. They find a mark and then go looking. The EPA's list of signs is short and worth knowing by heart.

The dark spots are the most useful of these, because they are hard to fake and easy to test. A bed bug spot is digested blood, so it soaks into fabric and spreads slightly at the edges. Dirt sits on top and brushes off. If a damp white cloth pulls a rusty smear out of the spot, that is a real sign.

Six bugs that look like bed bugs

This is the part that actually saves people money. The EPA leads its own control advice with it: make sure you really have bed bugs, not fleas, ticks or other insects. We have been called out to all six of the following, and three of them needed no treatment at all.

The two hardest are the first two, and they are hard for everybody. Colorado State University's own guidance is that separating bat bugs and swallow bugs from bed bugs takes close inspection with a hand lens or microscope. If a technician tells you they can call it across the room, they are guessing.

It is worth getting right, because the answer changes the whole job. Bat bugs came from a bat colony, usually in an attic or a soffit, and treating a mattress does nothing about that. The bugs will keep coming down the wall until the roost is dealt with.

The carpet beetle larva is the one we see most often, and it is the easiest to settle. Under a phone camera it is obviously hairy. The University of California's description of the varied carpet beetle larva is covered with dense tufts of hair, with alternating light and dark brown stripes, broader at the rear and narrower at the front. A bed bug is smooth, plain, and wider in the middle.

Where to actually look

Within about six feet of where somebody sleeps, and in seams rather than on open surfaces.

Texas A&M describes the pattern: they start in the tufts, seams and folds of the mattress and its cover, then spread to baseboards, window and door casings, picture moldings and furniture. In that order, and usually over months.

A real inspection is done with a flashlight held almost flat against the surface, so anything raised throws a shadow. Work through these, in this order:

• The mattress piping, all four sides, plus the tag and the handles.
• The box spring, which is better habitat than the mattress. Lift it and check the underside, including the stapled gauze.
• The bed frame joints, especially where two pieces bolt together, and every screw hole.
• The headboard, including the back and the wall behind it. This is the one most people never take off the wall.
• The nightstand, drawers out, turned over.
• Upholstered furniture where somebody regularly sleeps or naps. A recliner in a living room counts, and gets missed.

Two rules make the difference. Use a real flashlight, not a phone torch held straight on. And check the box spring properly, because on a lot of jobs it holds more than the mattress does.

When it is not a bug at all

Sometimes there is nothing to find, and that is a real answer rather than a failed inspection.

Texas A&M AgriLife publishes a guide for exactly this situation, Diagnosing Mysterious Bug Bites, and its list of non-insect causes is longer than most people expect. Enzyme-based detergents, fabric softeners, soaps, creams, makeup, deodorants and perfumes all show up on it. So do mold spores from houseplants and humidifiers, static electricity, and several medical conditions.

Its core instruction is the one we would give you too: it is essential to diagnose the cause of a problem before prescribing a treatment. Practically, that means catching a specimen. Tape or sticky traps along the edges of walls and under and around the bed work well. A&M also notes that vacuum bag contents are seldom helpful, which is worth knowing before you go to the trouble.

If you want a free second opinion that has nothing to sell you, Travis County has an AgriLife Extension IPM program staffed by an entomologist who will identify what you found.

Common questions