Key point in one sentence: You do not need to guess when identifying bed bugs: adults are about 5–7 mm, reddish-brown and flat (about the size of an apple seed), and only dark faecal spots, shed skins and bite marks together confirm an infestation; booklice and dust mites do not bite, so identifying the wrong insect only wastes time and money.
If you suspect your home has bed bugs (also called stink bugs or wood lice), the first step isn’t buying chemicals — it’s knowing what they look like. Many people mistake booklice or dust mites for bed bugs, and going in the wrong direction wastes time and money.
This guide is different from most articles: all the photos below are real photographs (sources: the US Centers for Disease Control and Prevention, Cornell University’s Integrated Pest Management Program and others — see the credits at the end), not AI-generated illustrations. Go through each sign one by one and learn to tell them apart.
1. Adults: Reddish-Brown, Flat, About 6 mm
According to the Centre for Health Protection, an adult bed bug is about 6 mm long, reddish-brown, with a flat oval body, and comes out at night to feed on human blood. Before feeding, the body is flatter; after a blood meal it swells up and turns a darker red.
How to tell: note that they have no wings and can’t jump — insects that jump are usually fleas, not bed bugs. When hiding, they like to squeeze into gaps: mattress seams, bed frame joints, behind the headboard.
2. Nymphs: Small, Pale and Semi-Transparent
A newly hatched nymph is only 1–2 mm, pale yellow and almost semi-transparent, and its abdomen shows red after a blood meal. Don’t think “small means it’s not a bed bug” — nymphs bite too, and they’re even harder to spot.
How to tell: they look just like adults (flat, oval, wingless), only smaller and paler. If you see a group of insects that all look the same but in different sizes, a whole colony is breeding there.
3. Eggs: Off-White, About 1 mm, Hidden in Cracks
Bed bug eggs are off-white, about 1 mm in size, and very hard to see with the naked eye. They are usually stuck together in groups of dozens, hidden in bed frame screw holes, cracks and mattress folds. According to the Centre for Health Protection, eggs hatch in about a week at room temperature — which is why bed bug treatment has to go on for several weeks; killing the adults isn’t the end of the job.
How to tell: shine a torch into the cracks — if you see a cluster of tiny off-white grains stuck fast and not moving, they’re very likely eggs. The photo below shows adults and eggs inside a wooden bed’s screw hole — exactly the kind of place that’s easiest to miss when checking.
Below is a microscopic close-up of an eggshell, showing its texture and shape:
4. Faecal Spots: Small Black / Rust-Coloured Spots That Stick Fast
This is the most common and easiest sign to recognise. After feeding, bed bugs excrete near their hiding places, leaving small black or rust-coloured spots stuck to bed frames, mattresses and wallpaper edges that won’t wipe off by hand (unlike ordinary stains). According to information compiled by the Consumer Council, dark red or rust-red excrement marks are an important clue for judging an infestation.
How to tell: the spots are tiny, appear in groups, and stick fast to the surface. The photo below shows faecal spots on a wooden bed board — if your wooden boards have similar black spots, check them seriously.
5. Shed Skins: Semi-Transparent Empty Shells — the Bug’s “Old Clothes”
Bed bugs moult 5 times as they grow from nymph to adult, leaving a semi-transparent empty shell each time. The shell looks exactly like the bug but is hollow and pale. Finding shed skins means bed bugs have lived and grown here.
How to tell: the empty shells are brittle and semi-transparent, and crumble when pressed — unlike live bugs, which spring back when pressed. They usually appear together with faecal spots.
6. Blood Stains: Small Blood Spots on Sheets
If you accidentally crush a bed bug while you sleep, the sheet is left with a small blood stain; bites can also bleed a little after feeding. Blood stains are usually small rust-red spots or smears, and they don’t stick fast the way faecal spots do.
How to tell: blood stains spread slightly into fabric, while faecal spots are solid black dots. If both appear together, the evidence for an infestation is strong. (Note: blood stains look different on different fabrics, and we can’t provide a real photo for this one — please go by the written description.)
7. Hiding Places in Practice: What a Severe Infestation Looks Like
Bed bugs hide during the day and come out at night, and their hiding places are close to where you sleep: mattress folds, bed frame gaps, behind the headboard, sofa gaps. The photo below shows a badly infested mattress — black faecal spots everywhere, and the white objects are eggs and shed skins. At this stage, DIY is very hard to manage and you need a professional pest control company.
Not Bed Bugs? Common Lookalikes
Booklice (psocids): Only 1–2 mm, pale yellow, and they like damp books, paper and wallpaper. Booklice don’t bite people — they only eat mould. If the “bugs” you see are around the bookcase more than the bed, they’re probably booklice, and fixing the dampness is enough.
Dust mites: Invisible to the naked eye (about 0.3 mm). They don’t bite, but their droppings can trigger a runny nose and skin allergies. If you’re itchy but can’t find any bugs or any of the signs above, it could be dust mites or an allergy — deal with that separately.
Fleas: They jump, are small and dark brown, and are usually brought in by pets; their bites concentrate on the ankles and calves. If you have pets and see jumping insects, think fleas first.
Remember the rule: only conclude it’s bed bugs once you’ve found two or more of the signs above, and only then start treatment. If you’re not sure, photograph it and ask a professional pest control company — don’t spray chemicals before you’ve confirmed the problem.
Further Reading
- DIY Bed Bug Removal in Hong Kong: A 6-Step Guide — what to do next, once you’ve identified them
- What Do Bed Bug Bites Look Like? Bite Identification and Handling FAQ — how to handle bites and when to see a doctor
- What Are Bed Bugs? Stink Bugs and Wood Lice — What’s the Difference? — the complete guide: what bed bugs are, and how the three names differ
- Bed Bug, Wood Louse or Stink Bug? Three Names, One Insect — how the three names differ
- How to Handle Clothes After Travelling Abroad? High-Temperature Drying Is the Only Way to Kill Eggs (Consumer Council and FEHD Temperatures Compared) — after a trip, how to handle clothes so you don’t bring bed bugs home
- FEHD “Ten Bed Bug Prevention Tips” Revisited: Airport Leaflets, Sealing Gaps at Home and Physical Egg-Killing Essentials — the FEHD’s official ten bed bug prevention tips
Photo Credits and Licences
All photos in this article are from Wikimedia Commons, and the licences have been verified:
- Adult, from above: © Louis-Marie Poissant, CC BY-SA 3.0
- Nymph: US Centers for Disease Control and Prevention (CDC), public domain
- Adult and eggs (wooden bed screw hole): © Thomas Oldani, CC BY 3.0
- Eggshell close-up: © Alexander Klepnev, CC BY 4.0
- Faecal spots: © NY State IPM Program at Cornell University, CC BY 2.0
- Shed skins: © Louis-Marie Poissant, CC BY-SA 3.0
- Severely infested mattress: © NY State IPM Program at Cornell University, CC BY 2.0
Sources
- Centre for Health Protection, “Bed Bugs (commonly known as bed bugs or wood lice)”: https://www.chp.gov.hk/tc/healthtopics/content/460/107441.html
- Food and Environmental Hygiene Department, “Guidelines on the Prevention and Control of Bed Bugs in Domestic Premises” (PDF): https://www.fehd.gov.hk/tc_chi/pestcontrol/library/pdf_pest_control/bedbugs(text).pdf
- Rentokil Hong Kong, “Signs of Bed Bugs”: https://www.rentokil.com/hk/blog/signs-of-infestation/signs-of-bed-bugs
- Consumer Council’s 6 bed bug control methods (via gotrip.hk): https://www.gotrip.hk/%E7%94%9F%E6%B4%BB%E7%99%BE%E7%A7%91/%E6%B6%88%E6%BB%85%E5%BA%8A%E8%9F%A8-%E6%BB%85%E8%9F%A8%E6%96%B9%E6%B3%95-gt12-358554/