What Bug Is This? Identify a Bug by Colour, Size and Where You Found It

Most unknown bugs can be narrowed to two or three candidates with three clues you already have: what colour it was, roughly how big, and where you found it. You do not need to know whether it was a beetle or a "true bug". Work through the three tables below, then confirm with the detail checks at the end.

One rule before you start: note the number of legs if you can. Six legs means an insect. Eight means a spider, tick or mite. Lots of legs means a centipede or millipede. That one count rules out half the list.

1. What colour was it?

Colour is the first thing people remember and the first thing they type into Google. Here are the usual suspects behind the most common descriptions. Sizes are body length without legs or antennae.

Two colour traps. A "red bug" on your skin that itches is almost never a bug you can still see: chiggers are microscopic and fall off within hours, so the red dot is the bite, not the animal. And a "black bug" seen at a distance is often dark brown up close; carpet beetles, bed bugs and small cockroaches all read as black in poor light.

2. How big was it?

Compare it with something on your desk rather than guessing millimetres.

• Pinhead or smaller (under 2 mm): mites, booklice, springtails, thrips, fungus gnats, newly hatched bed bugs and cockroaches. If it jumped when you touched it, springtail or flea.
• Sesame seed to apple seed (2 to 7 mm): adult bed bugs, fleas, carpet beetles, ants, weevils, fruit flies, drain flies, small spiders. This is the size range of nearly every indoor pest that matters.
• Fingernail (7 to 15 mm): house flies, cockroach nymphs, stink bugs, wasps, ladybirds, boxelder bugs, silverfish, earwigs.
• Larger than a fingernail: adult cockroaches, large beetles, centipedes, crickets, cicadas, large moths, hornets, most spiders people photograph.

Size and colour together do most of the work. A small brown bug the size of an apple seed with no wings is a bed bug until proven otherwise. A small brown bug the size of a sesame seed with a long snout is a weevil from the flour bag. Same colour, different problem.

3. Where did you find it?

Bugs are where their food and moisture are, so the room tells you a lot.

For a fuller room-by-room list of the 15 most common house bugs, with what each one means and what to do, see the house bug identifier.

Confirm it with four detail checks

Once you have two or three candidates, these settle it.

1. Legs. Six: insect. Eight: spider, tick or mite. Fourteen: pill bug or sow bug. Thirty or more: centipede (fast, flat) or millipede (slow, round).
2. Wings. Visible wings folded flat over the back: beetle, cockroach, stink bug, boxelder bug. No wings at all: bed bug, flea, silverfish, springtail, most nymphs. Two wings only: a fly.
3. How it moves. Jumps: flea, springtail, jumping spider, cricket. Scurries fast and hides: cockroach, silverfish, centipede. Flies toward light: moth, june beetle, stink bug, cluster fly. Barely moves: mealybug, scale, a full bed bug.
4. What it left behind. Dark specks on sheets: bed bugs. Pepper-like droppings in cabinets: cockroaches. Webbing in flour or cereal: pantry moths. Shed skins that look like the bug: silverfish, carpet beetle larvae, bed bugs.

Regional differences that change the answer

The same description points to different species depending on where you live.

• United States: boxelder bugs and brown marmorated stink bugs are the classic autumn window invaders. Brown recluse spiders exist only in the central and southern states.
• United Kingdom and Europe: firebugs (red and black, often in clusters at the base of lime trees) replace boxelder bugs. Harlequin ladybirds are the ones that come indoors in numbers. There are no medically significant spiders apart from a mild false widow bite.
• Australia and New Zealand: Christmas beetles, bronze orange bugs and huntsman spiders are everyday sights. Redback and funnel-web spiders are the two to take seriously; white-tailed spider bites are far less dangerous than their reputation.

When the bug matters

Most of the bugs above are a nuisance at worst. A few change what you do next.

• It bit you and you never saw it. Work through the pattern, location and timing of the bite in What bit me? before blaming a spider.
• Small, brown, flat, in the bed. Treat it as a bed bug until you have ruled it out with the bed bug identifier. Early action is the difference between a cheap fix and a professional treatment.
• Brown, fast, in the kitchen at night. Identify the species with the cockroach identifier; German cockroaches need professional treatment, an occasional American cockroach does not.
• Eight legs and you are worried. Most spiders are harmless. Is this spider dangerous? gives a four-question check that works in any region.

When the tables are not enough

Colour, size and location get you to a short list. A photo gets you to a name. If the bug is still there, photograph it from above in good light, as close as your phone will focus, with something for scale beside it. The Bug Identifier app identifies insects, spiders and their lookalikes from a single photo, tells you whether it bites or stings, and flags the few that are medically significant. If the bug is gone, photograph what it left behind: droppings, shed skins, damage and webbing identify many pests on their own.

Download Bug Identifier on the App Store and turn "what bug is this" into a name in seconds.

Frequently asked questions

What bug is small and black in my house?

Indoors, the usual answers are carpet beetles (round, on window sills and carpets), fungus gnats (fly weakly, near houseplants), drain flies (fuzzy, near sinks) and black ants. If it jumps, it is a flea or a springtail. Catch one on tape and look for the shape: round and beetle-like, long and fly-like, or flat and jumping.

What bug is red and black?

On walls and trees in autumn: boxelder bugs in North America, firebugs in Europe. In gardens: milkweed bugs and some ladybirds. All of these are harmless. A red and black bug with a soft body that leaves a blister when crushed is a blister beetle; do not handle it.

What bug is tiny and red?

Tiny red dots moving on a window sill in spring are clover mites, harmless but they stain when crushed. On houseplant leaves with fine webbing: spider mites. On your skin after a walk in long grass, red itchy welts with no visible bug: chiggers.

What is this bug in my bed?

Bed bugs are the first suspect: flat, oval, reddish-brown, apple-seed sized, with dark specks on the sheets nearby. Carpet beetle larvae (hairy, striped, slow) and booklice (tiny, pale) also turn up in bedding and are harmless. A spider is a visitor, not a resident.

Can I identify a bug from a picture?

Yes, and it is far more reliable than a description. A clear top-down photo shows the leg count, wing shape and markings that separate lookalikes. The Bug Identifier app does this from one photo; a good photo is also what a pest controller will ask for.