Start here: pattern, place, and pace
You usually don't need to see the bug to narrow it down. Three clues do most of the work: how many marks there are, where they sit on your body, and how fast they showed up.
Count and shape come first — a single itchy bump is different from a tight cluster, which is different from a neat line of two or three. Then location: ankles, the covered trunk, and exposed arms each point somewhere different. Finally timing — bites you only notice on waking suggest something that feeds at night, while marks that flare within minutes outdoors point to a daytime flyer.
Flying and biting insects (5)
These bite outdoors, in daylight or at dusk, and usually land on exposed skin.
- Mosquito — a single puffy, itchy bump that appears within minutes on exposed skin. The most common bite by far.
- Black fly — a swollen, sometimes bleeding bite around the head, neck, or hairline near moving water.
- Horsefly or deer fly — an instant sharp, painful bite that leaves a raised red welt, often on the legs or arms.
- Biting midge / no-see-um — tiny, intensely itchy bumps in loose groups, common near water at dusk.
- Stable fly — a sharp, painful jab usually on the lower legs and ankles; looks like a firm red spot.
Household and hidden biters (6)
These live in or near the home and often bite where you can't watch it happen.
- Bed bug — two to five bites in a line or zigzag, usually noticed on waking, on arms, shoulders, neck, or back.
- Flea — small red dots with an itchy halo, clustered low on the legs and around the ankles; common in homes with pets.
- Tick — a single spot where the tick attaches; a slowly expanding ring (a 'bull's-eye') is a reason to see a doctor.
- Chigger — very itchy clustered bumps where clothing is tight: sock lines, waistband, behind the knees.
- Mite (bird or rodent) — scattered itchy bumps, often after contact with nests, poultry, or a pet's bedding.
- Scabies mite — intense itching that's worse at night, with thin wavy tracks between the fingers and on the wrists; it needs prescription treatment.
Spider bites (3)
True spider bites are far less common than people think — most 'spider bites' turn out to be something else. When they do happen, these are the three that matter.
- Common house spider — usually two tiny puncture marks with mild redness that settles on its own.
- Black widow — a bite followed by muscle cramping and pain that spreads from the site; seek medical care.
- Brown recluse — a bite that becomes increasingly painful with a darkening center over several days; seek medical care. Found only in parts of the central and southern US.
Stings people search as 'bites' (6)
Technically these sting rather than bite, but they're what many people mean by 'what bit me' — so they belong on the chart.
- Bee — instant sharp pain with fast swelling; a honeybee may leave a stinger you can scrape out sideways.
- Wasp or hornet — sharp pain and rapid swelling; unlike bees they can sting more than once.
- Fire ant — a cluster of burning bumps that turn into small white pustules within a day.
- Other ant (bite-and-pinch) — a brief sting and a small red mark that fades quickly.
- Stinging caterpillar — a burning, itchy rash in the shape of wherever a fuzzy caterpillar brushed the skin.
- Jellyfish or sea creature — a stinging line or welt after swimming; included because beachgoers ask the same 'what bit me' question.
When any bite needs a doctor
Most bites on this list fade within a few days with nothing more than a cool compress and time. A small number are urgent. Get medical help right away if you notice any of the following, whichever bug you suspect.
- Trouble breathing, tightness in the throat, or swelling of the lips, tongue, or face.
- Dizziness, a racing heart, or feeling faint soon after a sting.
- Spreading redness, warmth, pus, or a red streak moving away from the bite.
- Fever, chills, body aches, or a spreading rash in the days after a bite.
- An expanding bull's-eye ring after a possible tick bite.
- Severe muscle cramps, or a wound with a darkening center, after a suspected widow or recluse bite.
Medical disclaimer. This page is for general information only. It is not a medical diagnosis. If you have severe symptoms — trouble breathing, swelling of the face or throat, fast spreading redness, fever, severe pain, pus, or signs of infection — contact a doctor or your local emergency number.