Summary
The brown recluse is one of two spider species in North America whose venom is established as capable of causing medically significant injury in humans. Its native range is tightly bounded - confirmed established populations occur in a band from southern Iowa through eastern Texas - and the species is frequently misidentified outside that range.
Quick answers
- Is Brown Recluse dangerous to humans?
- Yes. Brown Recluse is one of the few species in North America whose bite is established as medically significant. Adult-female bites can warrant medical evaluation.
- How big is an adult brown recluse?
- Adult female body length is 7–12 mm; males are 6–10 mm. Leg span reaches 20–30 mm.
- Where does Brown Recluse live?
- Undisturbed indoor spaces - closets, attics, basements, behind furniture, inside cardboard boxes and shoes. Outdoors found under bark, rocks, and debris. Established U.S. populations occur in 16 states.
- What does Brown Recluse eat and when is it active?
- Small soft-bodied insects including cockroach nymphs, crickets, and silverfish. Will scavenge dead prey. Nocturnal. Hunts on foot rather than from webs. Adults peak March–October.
Identification
- Six eyes in three pairs (most spiders have eight)
- Uniform tan to dark brown coloration; legs slightly darker, no banding or stripes
- Dark violin-shaped marking on cephalothorax with neck pointing toward abdomen (subtle in juveniles)
- Body 6–12 mm; leg span about the size of a U.S. quarter (25 mm)
- Smooth, fine hairs - no spines on legs
- Long, thin legs of uniform color (no joint banding)
Morphometrics
| Measurement | Female | Male |
|---|---|---|
| Body length | 7–12 mm | 6–10 mm |
| Leg span | 20–30 mm | - |
| Lifespan | 1–4 years | - |
| Trait | Value |
|---|---|
| Web type | Irregular, loose, off-white sheet web used as a daytime retreat - not for prey capture. |
| Eye arrangement | Six eyes arranged in three pairs (dyads) forming a semicircle - the single most reliable identifying trait. |
| Eggs per sac | 40–50 |
| Egg sacs per year | 1–5 |
Geographic range
Native range: South-central United States, from southern Iowa and Nebraska south to Texas, east to western Georgia.
U.S. states with established populations: Alabama, Arkansas, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Nebraska, Ohio, Oklahoma, Tennessee, Texas.
State pages covering Brown Recluse
AlabamaArkansasGeorgiaIllinoisIndianaIowaKansasKentuckyLouisianaMississippiMissouriNebraskaOhioOklahomaTennesseeTexas
Habitat & behavior
Habitat: Undisturbed indoor spaces - closets, attics, basements, behind furniture, inside cardboard boxes and shoes. Outdoors found under bark, rocks, and debris.
Activity: Nocturnal. Hunts on foot rather than from webs. Adults peak March–October.
Diet: Small soft-bodied insects including cockroach nymphs, crickets, and silverfish. Will scavenge dead prey.
Venom & medical significance
| Venom property | Value |
|---|---|
| Type | Cytotoxic (sphingomyelinase D) |
| LD₅₀ | Approx. 1.45 mg/kg (mouse, intraperitoneal) for purified sphingomyelinase D |
| Note | Most bites heal without medical intervention; loxoscelism (necrotic ulcer) occurs in a minority of confirmed cases. |
Bite symptoms & first aid
Symptoms
- Initial bite usually painless; pain develops 2–8 hours later
- Localized redness, swelling, and a developing bullseye lesion within 24–48 hours
- In a minority of cases: necrotic ulcer that may take weeks to heal
- Systemic loxoscelism (rare): fever, chills, hemolysis - more common in children
Commonly confused with
- Wolf spider
- Southern house spider
- Grass spider
- Cellar spider
- Yellow sac spider
Key facts
Sources
- [1]Causes of necrotic wounds other than brown recluse spider bites - Toxicon (Vetter & Bush, 2002). Accessed 2026-06-14.
- [2]Spiders Found in or near Homes (Publication 7468) - UC Statewide IPM Program. Accessed 2026-06-14.
- [3]Brown Recluse Spider - University of Kentucky Entomology (ENTFACT-631). Accessed 2026-06-14.