The short answer
Bed bugs are wingless, flattened, oval insects of about 5 mm, reddish brown in colour, that hide by beds and sofas and take blood at night. An adult carpet beetle is a small rounded beetle, about 2 to 4 mm, often mottled brown, white and yellow, that flies to windows; its larva is a bristly brown grub found in carpets and wardrobes. Bed bugs bite; carpet beetle larvae do not, though their hairs can irritate skin.
Carpet beetles are one of the commonest reasons people think they have bed bugs. Both are small and brownish, both turn up in bedrooms, and both can leave you with itchy skin. But they are very different animals, need different treatment, and one costs a great deal more to deal with than the other. A few minutes with a torch and a magnifying glass usually tells you which you have.
The quick comparison
| Bed bug | Carpet beetle | |
|---|---|---|
| What it is | A true bug that feeds only on blood | A beetle; the larvae eat wool, fur, feathers and dead insects |
| Adult shape | Flat and oval, like an apple pip | Rounded and domed, like a tiny ladybird |
| Adult size | About 5 mm | About 2 to 4 mm, depending on species |
| Adult colour | Even reddish brown, darker after feeding | Often mottled brown, white and yellow scales |
| Wings | None; cannot fly | Yes; adults fly and gather at windows in spring and summer |
| Young | Paler, smaller copies of the adult | Bristly, banded brown grubs called woolly bears |
| Where you find them | Mattress seams, bed frames, headboards, sofas | Carpet edges, under furniture, wardrobes, airing cupboards, near old birds’ nests |
| Active | At night, when you are asleep | Adults in daylight; larvae hidden and slow |
| Skin effect | Bites, often in lines or clusters | Does not bite; bristles on the grubs irritate some people’s skin |
Looking at the adults
Put the insect on a white sheet of paper and look at it side on.
A bed bug is strikingly flat, so it can slip into a seam or behind a skirting board. It has no wings, a broad oval body and short legs, and moves at a steady walk. Unfed, it is light brown; after feeding it swells and turns deep red-brown. The NHS describes them as yellow, red or brown.
An adult carpet beetle is the opposite: round, hard and domed. The varied carpet beetle, the commonest in British homes, has a pattern of brown, white and yellowish scales that rub off with handling, so an old specimen may look plain dark. Adults fly well and are often found on windowsills, because they head for the light to get outdoors and feed on pollen.
Looking at the young
This is where mix-ups usually happen, because people find larvae, not adults.
Young bed bugs look like smaller, paler versions of the adult, almost see-through before they feed. They are found in the same places as adults, close to where people sleep.
Carpet beetle larvae look nothing like bed bugs once you see them close up. The Natural History Museum describes the varied carpet beetle larva as about 4 to 4.5 mm long, covered in hairs, with tufts at the tail, banded in shades of brown. They move slowly and curl when disturbed. You may also find their empty bristly cast skins, which some people mistake for bed bug skins.
The bites and the rash
Bed bugs bite exposed skin at night. Bites are often in a line or a small cluster on the arms, neck or legs. People react very differently: some get large itchy welts, others nothing at all.
Carpet beetles do not bite. Some people, though, are sensitive to the fine bristles on the grubs and break out in itchy bumps wherever skin has rested on affected bedding, clothes or carpet. A 2024 review in the journal Cutis describes this reaction, which is easily mistaken for bites.
So a rash alone does not tell you which insect you have. Only the insect, or its droppings and skins, can.
Other clues
- Dark spots on the mattress that smear when wiped point to bed bugs. Carpet beetles do not leave them.
- Small round holes in woollen jumpers, rugs or felt, with no webbing, point to carpet beetles.
- Insects on the windowsill in spring or summer are far more likely to be adult carpet beetles.
- Bites appearing after a stay away or a second-hand furniture purchase point towards bed bugs.
Why it matters which one you have
The treatments are different. Carpet beetles are usually dealt with by finding the source, often under a carpet edge, in a wardrobe or an old bird’s nest in the loft, then vacuuming thoroughly, washing or freezing affected textiles and, if needed, a targeted professional treatment.
Bed bugs need a planned treatment of the bed, the furniture around it and nearby rooms: a spray course or a heat treatment. Paying for a bed bug treatment when the problem is carpet beetles wastes money, and the other way round leaves bed bugs to spread.
If you are still not sure
Trap one in a sealed jar or a zip bag. Colorado State University’s guide to bed bug look-alikes is a useful second opinion, and a specialist can identify it in seconds. If you want certainty before paying for treatment, an inspection gives a written answer.
If it does turn out to be bed bugs, you can send a request below for a specialist who covers your part of Birmingham.