The guide
What kind of bug is this?
It is the question almost nobody can answer at the moment they need to. Something is on the bathroom wall at midnight, or under a plant pot, or on a child’s arm, and what you want is not its taxonomic order. You want to know whether to worry.
Upload a photo above and you get that answer first: what it is, whether it can hurt you, and — the part most tools skip — what else it could have been. A harmless verdict is only reassuring if you know what was considered and ruled out.
How to photograph a bug so it can actually be identified
Most failed identifications are failed photographs. The animal is small, it is moving, and the phone focuses on the wall behind it. Four things make the difference:
- Get the whole animal in frame, side-on if you can. Leg length and body proportions carry more information than colour, and a top-down shot hides both.
- Fill the frame, then step back slightly.Phone cameras cannot focus closer than about 10 cm. Getting close and cropping afterwards beats a blurred close-up.
- Put something for scale in the shot— a coin, a fingertip, the edge of a tile. Size is one of the strongest separators and one of the hardest things to judge from a photo.
- Use the flash, even in daylight. It freezes movement and lifts the markings on the back and legs that identification actually turns on.
If the animal is a spider and you can safely photograph it from the front, do. The arrangement of the eyes is the single most reliable character in the group, and it is the one thing that separates a brown recluse from the four harmless spiders it is mistaken for.
Identify a bug by picture, or work it out yourself
You do not need a tool for the first step. Count the legs, and you have already narrowed it to a handful of possibilities:
- Six legs, three body sections, usually antennae.An insect — beetles, ants, wasps, moths, true bugs.
- Eight legs, two body sections, no antennae.An arachnid — spiders, and scorpions if it has pincers and a tail.
- Many legs, one pair per segment. A centipede. Fast, flattened, and a predator.
- Many legs, two pairs per segment. A millipede. Slow, round in cross-section, and harmless.
- A soft segmented body with stubby legs. A caterpillar, which is a larva rather than an adult and often looks nothing like the moth it becomes.
Getting the group right matters more than getting the species right, because almost every dangerous misidentification starts with a wrong group. A spider called a fly, or a widow called an orb weaver, cannot be rescued by anything downstream.
The ones worth ruling out first
The number of arthropods in the United States that can genuinely harm a healthy adult is small. These are the ones the whole question usually comes down to:
Everything else you are likely to find indoors is, in the plainest terms, fine. Of the 16 spiders documented here, most are harmless and several are actively useful — a cellar spider in the corner of a ceiling is eating the things you would rather not have.
What people get wrong most often
The brown recluse.It is the most over-reported spider in America by a wide margin. Nearly every “recluse” turns out to be a southern house spider, a barn funnel weaver or a wolf spider. The violin marking is far less reliable than its reputation; the eyes are what settle it, and its range is much smaller than most people assume.
The daddy long legs myth. The story that cellar spiders have the most powerful venom of any spider but fangs too short to use is untrue in both halves. They have neither.
Fuzzy means friendly. Not with caterpillars. A woolly bear will walk across your hand, but a puss caterpillar looks like a scrap of cotton wool and delivers one of the most painful stings of any insect in North America. Children pick them up precisely because they look strokeable.
Hobo spiders. They were blamed for necrotic wounds for years. The evidence did not hold up, and the CDC removed the hobo spider from its venomous spiders list in 2017. A lot of the internet has not caught up.
What this identifier will not tell you
Plenty of photographs simply do not contain the answer. If a spider is a nondescript brown male photographed from above, the eye arrangement is not visible, and no identifier — ours or anyone else’s — can separate a recluse from a funnel weaver on that image. When we hit that wall we say so, and we will not publish a harmless verdict we cannot stand behind.
We also do not give medical advice or pest control advice. We identify. If you have been bitten or stung and symptoms develop, see a doctor. You can read exactly how accurate the identifier is, measured against 168 expert-verified photographs, including the cases it still gets wrong.
Common questions
Is this bug identifier free?
Yes. There is no account, no signup and no paywall. Upload a photo and you get the answer.
What happens to my photo?
Your browser sends a resized, metadata-free copy. Know That Bug never writes it to storage and discards its in-process copy once the answer returns. We keep a one-way hash and the identification, never a reconstructable picture — our processor’s retention is explained in privacy.
Why does it sometimes refuse to say “harmless”?
Because the photograph did not support it. If an answer lands in a group that recluses, widows or bark scorpions are routinely mistaken for, and the image does not resolve the character that would rule them out, you get an explicit “we can’t rule this out” instead. Being told a harmless spider might not be costs you a moment of caution. The reverse costs considerably more.
Why don’t you show a confidence percentage?
Because a decimal implies a precision nobody in this field has. We publish three bands instead, and the measured accuracy of each. High confidence means 95.7% correct to genus. Low means 32.4%, and we would rather tell you that than dress it up.
Can it identify a bug bite?
Not reliably from the mark alone. Most bites and skin reactions look too similar to identify the animal safely. Our bug bite and sting guide explains what different species can cause, but the reliable route is to photograph the animal itself.
Does it work outside the United States?
It will often identify the animal correctly, but the danger assessment and the lookalike comparisons are written for US species. Treat a result from elsewhere as a starting point.
Start with the insect identifier, the spider identifier or the caterpillar identifier, or read how we identify.
mayfly1963 · CC-BY