Bug Bite Identifier

The honest answer first: a bite cannot reliably be identified from a photograph of the bite. What we can do is work backwards from the animal.

Safety review: 3 August 2026 · US-focused guidance; emergency and poison-control services differ elsewhere.

Why we won’t identify a bite from a photo

A mark on skin carries far less information than the animal that made it. Most bites look like a small red bump, and a mosquito, a flea, a spider and a bacterial infection can all produce something indistinguishable. Worse, the reaction depends more on the person than the species — two people bitten by the same spider on the same evening can end up with completely different marks.

Any tool that looks at a photo of your arm and names a species is guessing, and a confident wrong answer here is the most dangerous thing this site could produce. So we don’t.

Stop reading and get help if

Call emergency services now for difficulty breathing, swelling of the face or throat, fainting, a seizure, or severe weakness.
In the US, call Poison Control at 1-800-222-1222 after a known or suspected scorpion sting, a severe caterpillar sting, or when you are unsure what level of care is needed.
Contact a clinician promptly for severe or spreading pain, muscle cramping, repeated vomiting, a worsening wound, or a new rash or fever after a tick bite.

We identify animals; we do not diagnose skin marks or give medical treatment advice. If symptoms are severe or worsening, use a medical service rather than waiting for an online identification.

Start with the animal, not the mark

If you saw what bit you, or you can find it, that settles the question far more reliably than any bite chart. Photograph the animal and we will identify it, then tell you what its bite actually does.

These are the species in our guide whose bite or sting is medically significant:

Arizona Bark Scorpion Centruroides sculpturatus
Black Widow Latrodectus mactans
Brown Recluse Loxosceles reclusa
Brown Widow Latrodectus geometricus
Puss Caterpillar Megalopyge opercularis
Amazonian Giant Centipede Scolopendra gigantea
Tick Ixodes scapularis

What each one actually does

Every entry below is taken from that species’ own record, where you will also find the sources it was checked against.

Arizona Bark Scorpion Medically significant

Looks like: There is often little to see — sometimes no mark at all, sometimes slight redness and swelling. The absence of a visible wound does not mean the sting was minor.

Feels like: Immediate, intense burning pain, often with numbness or tingling that spreads. In more severe cases, particularly in children, there can be muscle twitching, difficulty swallowing, blurred vision and agitation.

Black Widow Medically significant

Looks like: Often unremarkable at the site: a small red mark, sometimes with two faint punctures and a pale ring. The bite site is not the point with a widow — the systemic effects are.

Feels like: A sharp pinprick, then severe muscle pain and cramping that spreads from the bite over the following hours, often to the abdomen or back. Sweating, nausea and a raised heart rate are common.

Brown Recluse Medically significant

Looks like: Most bites cause a small red mark that heals on its own. A minority develop into a slow-healing ulcer over several days, sometimes with a pale centre and a darker rim. Crucially, a great many wounds diagnosed as recluse bites turn out to be something else entirely — bacterial infections in particular look very similar and are far more common.

Feels like: Usually painless at the moment it happens. Soreness typically develops over the following few hours rather than immediately.

Brown Widow Medically significant

Looks like: Usually a small red mark with local swelling. Brown widow bites tend to stay local rather than producing the widespread cramping a black widow can cause, which is thought to be because less venom is delivered.

Feels like: A sharp sting followed by aching around the site. Systemic effects are possible but much less common than with a black widow.

Puss Caterpillar Medically significant

Looks like: A grid or train-track pattern of red marks matching where the spines touched, with swelling that can spread well beyond the contact point.

Feels like: Immediate intense throbbing pain, often radiating up the limb, and frequently described as one of the worst stings of any North American insect. Nausea, headache and swollen glands can follow.

Amazonian Giant Centipede Medically significant

Looks like: Two puncture marks may be present, with redness and swelling around the site. Appearance alone cannot show how severe an envenomation is.

Feels like: Immediate burning pain that can be severe and can spread up the affected limb. Scolopendra pain may persist for hours or longer.

Tick Medically significant

Looks like: Often nothing at first beyond the attached tick. A small red mark may follow. An expanding circular or bull's-eye rash appearing days to weeks later is a recognised sign of Lyme disease and is not an allergic reaction to the bite.

Feels like: Often painless, which is why ticks are usually found by sight rather than by feel.

False Widow Painful

Looks like: A red mark with local swelling that fades within a day or two. It does not ulcerate.

Feels like: A sharp sting at the time, with soreness for a few hours. Some people report a dull ache in the limb, but the widespread cramping of a true widow bite does not occur.

Hobo Spider Painful

Looks like: Most bites produce nothing more than a small red mark, much like a mosquito bite, which fades over a few days. The dramatic necrotic wounds once attributed to this species have not held up to investigation, and many were later traced to infections or to other causes entirely.

Feels like: Often not felt at all. Where it is, people describe a brief sharp prick followed by mild soreness.

Desert Hairy Scorpion Painful

Looks like: Local redness and swelling at the sting site.

Feels like: Comparable to a bee sting: sharp at the time, then aching and sore for a few hours. Widespread effects are not expected.

Hickory Tussock Moth Painful

Looks like: An itchy red rash where the hairs contacted skin, sometimes with small raised bumps. Reactions vary a lot between people; many feel nothing at all.

Feels like: Itching and mild stinging rather than sharp pain. It usually settles within a day.

Io Moth Caterpillar Painful

Looks like: Red welts along the line of contact, often with a nettle-like rash and some swelling around it.

Feels like: Immediate stinging and burning, comparable to a nettle but stronger, usually easing over a few hours.

Saddleback Caterpillar Painful

Looks like: A row or patch of red welts where the spines made contact, often with swelling and sometimes a nettle-like rash spreading a little beyond.

Feels like: Immediate burning that builds over several minutes, then throbs. It typically eases within a few hours, though the rash can last a day or two.

Striped Bark Scorpion Painful

Looks like: Often little to see: mild redness and slight swelling at the sting site, sometimes nothing at all.

Feels like: Immediate sharp burning pain with numbness or tingling around the site, typically easing over several hours. Widespread symptoms are uncommon in healthy adults.

Yellow Sac Spider Painful

Looks like: A red mark with mild local swelling, sometimes with two faint puncture points. It can stay sore and slightly raised for a few days. It was long blamed for necrotic wounds; that link has not held up under investigation.

Feels like: Sharper than most spider bites, often described as a sting that wakes people up, followed by an itchy ache.

Woodlouse Spider Painful

Looks like: A pair of small puncture marks with local redness, sometimes with mild swelling. It settles within a day and does not ulcerate.

Feels like: A sharp sting at the time, comparable to a bee, fading to soreness over an hour or two.

Tarantula Hawk Painful

Looks like: Very little to see. A small puncture with local redness that fades within a day. The sting site is not the story here.

Feels like: Immediate, overwhelming, electric pain that peaks within seconds and subsides substantially after about five minutes. The standard advice from the entomologist who ranked it is simply to lie down and shout, because you will not be capable of anything useful and falling over is the real risk.

Velvet Ant Painful

Looks like: A small puncture with local redness and swelling. There is very little to see relative to how much it hurts.

Feels like: Immediate, sharp, burning pain out of all proportion to the animal's size, easing substantially within about half an hour.

Yellowjacket Painful

Looks like: Immediate redness and a raised weal, often with a visible puncture. Swelling can be considerable and still be a normal local reaction.

Feels like: Sharp burning pain at the moment of stinging, easing to an ache and an itch over several hours.

Paper Wasp Painful

Looks like: A red weal with local swelling, fading over a day or two.

Feels like: Sharp pain at the sting, settling into an ache and itch. Generally reported as more painful in the moment than a yellowjacket sting.

Red Wasp Painful

Looks like: A red weal with swelling, usually settling within a day or two.

Feels like: Sharp and hot, often described as worse than a yellowjacket sting, easing to a deep ache over a few hours.

Bald-faced Hornet Painful

Looks like: A red weal with pronounced local swelling, sometimes for several days.

Feels like: Sharp, hot pain. Multiple stings are common in an encounter because the colony responds together and each wasp can sting more than once.

Fire Ant Painful

Looks like: Immediate red weals, then within roughly 24 hours a small white or yellow pustule at each sting. Often in a ring or arc from one ant pivoting. The pustule is characteristic of fire ants specifically.

Feels like: An immediate burning sting, which is where the name comes from, followed by intense itching for several days.

Harvester Ant Painful

Looks like: A red weal with swelling that can spread along the limb, and can persist for several hours. No pustule, which distinguishes it from a fire ant.

Feels like: Intense, deep, radiating pain that builds and can last several hours — long out of proportion to the size of the animal.

Bed Bug Painful

Looks like: Small red raised marks, often in a line or a loose cluster, on skin exposed while sleeping. Reactions vary enormously — some people show nothing at all.

Feels like: Painless at the time. Itching develops over hours to days, and the delay is why people rarely connect the bite to the night it happened.

Flea Painful

Looks like: Small red spots, often with a darker centre, usually in clusters around ankles and lower legs. Some people react strongly and some barely at all.

Feels like: A sharp small itch, immediate rather than delayed, and persistent for several days.

Carolina Wolf Spider Harmless

Looks like: Rare. A large individual can break skin, leaving two puncture marks with local redness and swelling that settles within a day or two.

Feels like: Comparable to a wasp sting, with a dull ache afterwards.

Banana Spider Harmless

Looks like: Rare, and mild. A bite produces localised redness and a small welt, much like a bee sting without the swelling, and settles within a day.

Feels like: A sharp momentary sting rather than lasting pain.

Jumping Spider Harmless

Looks like: Bites are rare enough to be a curiosity. Where one happens it leaves a small red mark comparable to a nettle sting, and it fades within a day.

Feels like: A brief pinprick, if anything at all.

Yellow Garden Spider Harmless

Looks like: Very rarely bites. Where it does, the result is a small red mark and mild local swelling that clears within a day or so.

Feels like: Comparable to a bee sting, without the lasting ache.

Common questions

Can you tell what bit me from a picture of the bite?

No, and neither can anyone else reliably. Identify the animal instead — that is a question a photograph can actually answer.

I woke up with bites in a row. What does that mean?

Lines or clusters of small itchy bumps appearing overnight are much more often insects that feed while you sleep than spiders. Spiders bite defensively, usually once, and rarely in a neat pattern. That said, patterns are suggestive rather than diagnostic.

How do I know if it was a spider?

Usually you don’t, unless you saw it. Spider bites are far less common than the internet suggests, and a great many wounds attributed to spiders — particularly to brown recluses— turn out to be bacterial infections, which look very similar and are far more common.

Should I bring the spider to the doctor?

If you can do it safely, yes. A specimen removes all the guesswork, and it is the single most useful thing you can hand over.

Safety sources

The escalation language above was checked against these US public health and poison-information sources. Each species page lists the references used for its individual danger and bite claims.

CDC/NIOSH — Venomous spiders (checked 3 August 2026)
CDC — What to do after a tick bite (checked 3 August 2026)
Poison Control — Scorpion stings (checked 3 August 2026)
University of Florida IFAS — Puss caterpillar (checked 3 August 2026)