Spider identification key
Answer whatever you can — every question is optional. Widows and recluses stay pinned to the top of the results for as long as they remain possible, so the moment the banner turns from red to violet you have your answer.
1.Was there a web, and what shape?
optionalThe most informative question. Web architecture is fixed by family, so it separates the big groups immediately — and it rules out recluses and widows faster than anything else.
2.Which state are you in?
optionalMatters more than you would expect. Brown recluses are absent from most of the country, including California, Florida and the entire northeast.
3.How big was the body?
optionalBody only, not counting the legs. Neighbouring sizes stay on the list, because everyone overestimates.
4.Where did you find it?
optionalIndoor and outdoor spiders barely overlap, so this cuts the list roughly in half.
5.Any distinctive markings?
optionalA red hourglass underneath means a widow and nothing else. A violin shape is suggestive of a recluse but far from conclusive — several harmless spiders have similar marks.
6.Did it do any of these?
optionalBehaviour separates families cleanly. Jumping means a jumping spider; eyes reflecting a torch beam means a wolf spider.
7.What colour was it?
optionalLast, and it never removes anything from the list — spider colour varies with age, moult stage and light.
- Brown RecluseSee a doctorLoxosceles reclusa
- Brown WidowSee a doctorLatrodectus geometricus
- Desert RecluseSee a doctorLoxosceles deserta
- Northern Black WidowSee a doctorLatrodectus variolus
- Southern Black WidowSee a doctorLatrodectus mactans
- Western Black WidowSee a doctorLatrodectus hesperus
- American House SpiderHarmlessParasteatoda tepidariorum
- Black and Yellow Garden SpiderHarmlessArgiope aurantia
- Bold Jumping SpiderHarmlessPhidippus audax
- Cross OrbweaverHarmlessAraneus diadematus
- Dark Fishing SpiderHarmlessDolomedes tenebrosus
- False WidowStings onlySteatoda grossa
- Giant House SpiderHarmlessEratigena duellica
- Golden Silk OrbweaverHarmlessTrichonephila clavipes
- Goldenrod Crab SpiderHarmlessMisumena vatia
- Grass SpiderHarmlessAgelenopsis species
- Green Lynx SpiderHarmlessPeucetia viridans
- HarvestmanHarmlessOrder Opiliones
- Hobo SpiderHarmlessEratigena agrestis
- Joro SpiderHarmlessTrichonephila clavata
- Long-bodied Cellar SpiderHarmlessPholcus phalangioides
- Marbled OrbweaverHarmlessAraneus marmoreus
- Nursery Web SpiderHarmlessPisaurina mira
- Southern House SpiderHarmlessKukulcania hibernalis
- Spiny-backed OrbweaverHarmlessGasteracantha cancriformis
- Texas Brown TarantulaHarmlessAphonopelma hentzi
- Wolf SpiderHarmlessTigrosa and Hogna species
- Woodlouse SpiderStings onlyDysdera crocata
- Yellow Sac SpiderStings onlyCheiracanthium inclusum
- Zebra Jumping SpiderHarmlessSalticus scenicus
If you think you were bitten
- Most suspected spider bites are not spider bites. Studies of patients presenting with a “spider bite” repeatedly find that the large majority are bacterial skin infections — frequently MRSA — which need antibiotics rather than reassurance. A spreading, painful, pus-filled sore is far more likely to be an infection than a spider.
- Wash it, ice it, and watch it. Clean the area with soap and water, apply a cold pack, and keep an eye on it.
- Get medical care if the wound spreads or darkens, if you develop cramping, sweating, fever or severe abdominal pain, or if you are confident it was a widow or a recluse.
- Bring the spider only if it is already dead and to hand. Do not go looking for it. Doctors treat symptoms, not species.
In the US, the Poison Help line is 1-800-222-1222. This site is a reference, not medical advice.