The short answer
Fleas are smaller, narrow from side to side and jump, and they are usually brought in by pets, with bites mostly around the ankles. Bed bugs are larger, broad and oval, cannot jump, and hide in and around the bed, biting skin that is uncovered while you sleep. Telling them apart matters because the treatment is different.
You wake up with itchy red marks and spot something small and dark on the sheet. Is it a flea or a bed bug? The two get mixed up all the time, partly because both feed on blood and both leave bites that itch.
They are different insects, though, and they need different treatment. This guide compares them side by side so you can make a sensible first guess, and explains why it is worth getting a professional to confirm.
The quick comparison
The table below draws on the US National Pest Management Association (NPMA), the University of Kentucky, the BPCA and NHS 111 Wales.
| Bed bugs | Fleas | |
|---|---|---|
| Size | About 5mm, up to 6mm (sources vary) | No more than about 3mm |
| Shape | Broad, flat and oval, like an apple pip | Narrow, flattened from side to side |
| Colour | Reddish brown | Brown-black, can look reddish after feeding |
| How they move | Crawl; cannot fly or jump | Jump, using long back legs |
| Where you find them | Mattress seams, bed frames, behind headboards, sofas | On pets and where pets rest |
| Where bites appear | Skin uncovered in bed: face, neck, arms, hands | Mostly ankles and lower legs |
| Usually brought in by | People: luggage, second-hand furniture, clothing | Pets, or animals living nearby |
Size and shape
Size is the first clue, though both are small enough that it helps to look closely. The NPMA puts adult fleas at no more than about 3mm (1/8 inch) and adult bed bugs at about 5mm (3/16 inch). The BPCA’s leaflet says adult bed bugs reach up to 6mm, so you will see figures from 5mm to 6mm depending on the source. Young bed bugs are smaller and paler, which can add to the confusion.
Shape is often more useful than size. A flea is thin when seen from above, because its body is squashed from side to side so it can move through fur. A bed bug is the opposite: wide, flat and oval when seen from above, a bit like a lentil or an apple pip.
How they move
Fleas are built for jumping. If a small insect springs away when you go to touch it, it is very likely a flea.
Bed bugs cannot fly or jump. They crawl, and not especially quickly. If what you found was walking slowly along a mattress seam or the edge of a headboard, that points towards bed bugs.
Where you find them
Fleas
Fleas live on animals and in the places animals rest. The NPMA notes they are often brought into the home by pets. A dog or cat scratching more than usual, or bites that started after a pet came back from somewhere, are good clues. Fleas can also come from wildlife or a previous tenant’s pet.
Bed bugs
Bed bugs hide near where people sleep or sit for long periods. Look along mattress seams, around the bed frame, behind the headboard and in sofas. NHS 111 Wales lists small spots of blood on bedding and small brown spots on bedding or the mattress as signs. Bed bugs arrive with people rather than pets, usually in luggage, bags, clothing or second-hand furniture.
Flea bites vs bed bug bites
Bites on their own are not a reliable way to tell, because people react so differently. Some people get large itchy welts and others notice nothing. Still, where the bites are can help.
Where flea bites usually appear
The University of Kentucky says flea bites are mainly found around the ankles and lower legs. That makes sense: fleas jump up from the floor or a pet’s bedding.
Where bed bug bites usually appear
Bed bugs bite whatever skin is uncovered while you are in bed. NHS 111 Wales mentions the face, neck, arms and hands. Kentucky makes a similar point, noting that bed bugs bite any exposed skin.
If bites are very itchy, look infected or are not settling down, a pharmacist can advise, or speak to your GP. The CDC says bed bugs are not known to spread disease, which is some comfort, but bites can still be very uncomfortable.
Why telling them apart matters
Getting this right saves time and money, because the two are dealt with in quite different ways.
- Fleas mean treating your pets as well as your home. Speak to your vet about treating cats and dogs, and keep the treatment up to date.
- Bed bugs have nothing to do with pets. Treating the dog will not help. The BPCA says self-treatment is unlikely to succeed, and the NHS says bed bugs are very difficult to get rid of yourself, so professional treatment is advised.
Avoid shop sprays and foggers for either problem until you know what you are dealing with. They rarely solve a bed bug problem and can spread the bugs into new hiding places.
Getting a clear answer
If you are not sure, the simplest step is to have someone who sees these insects every day take a look. A bed bug inspection will confirm whether you have bed bugs, fleas or something else, and how far it has spread. If it is bed bugs, our cost calculator gives a rough guide to price, and we can help you find a bed bug exterminator nearby.
You might also find our guides on whether bed bugs can live in your hair and how long bed bugs live useful.
If you have found signs at home, tell us where you are and we will find an exterminator who covers your area.