Yellow Sac Spider (Cheiracanthium inclusum) - Identification, Range & Medical Data

Summary

A small pale spider commonly found indoors throughout North America. Although its bite is sometimes painful and was historically blamed for necrotic lesions, current evidence suggests true necrosis is rare.

Quick answers

Is Yellow Sac Spider dangerous to humans?: Sometimes. Yellow Sac Spider bites are usually self-limiting, but a minority of cases produce notable local symptoms. Most do not require medical care.
How big is an adult yellow sac spider?: Adult female body length is 5–10 mm; males are 4–8 mm. Leg span reaches 16–25 mm.
Where does Yellow Sac Spider live?: Indoors on walls and ceiling corners; outdoors on vegetation. Notorious for being attracted to volatile hydrocarbons (linked to vehicle fuel line blockages). Established U.S. populations occur in 1 states.
What does Yellow Sac Spider eat and when is it active?: Small soft-bodied insects, other spiders, insect eggs. Nocturnal active hunter. Drops to the floor and runs when disturbed.

Identification

Pale yellow to greenish-tan body, 5–10 mm
Dark fang area contrasting with pale body
Long, prominent front legs
Builds a small silk retreat sac where wall meets ceiling
No web for prey capture

Morphometrics

Measurement	Female	Male
Body length	5–10 mm	4–8 mm
Leg span	16–25 mm	-
Lifespan	1–2 years	-

Trait	Value
Web type	No prey-capture web; builds a small silk retreat sac in ceiling corners or under leaves.
Eye arrangement	Eight eyes in two rows of four, roughly equal in size.
Eggs per sac	30–50
Egg sacs per year	1–5

Geographic range

Native range: Throughout the continental United States and southern Canada.

U.S. states with established populations: All 48 contiguous U.S. states.

State pages covering Yellow Sac Spider

Alabama Alaska Arizona Arkansas California Colorado Connecticut Delaware Florida Georgia Hawaii Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hampshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas Utah Vermont Virginia Washington West Virginia Wisconsin Wyoming

Habitat & behavior

Habitat: Indoors on walls and ceiling corners; outdoors on vegetation. Notorious for being attracted to volatile hydrocarbons (linked to vehicle fuel line blockages).

Activity: Nocturnal active hunter. Drops to the floor and runs when disturbed.

Diet: Small soft-bodied insects, other spiders, insect eggs.

Venom & medical significance

Venom property	Value
Type	Cytotoxic activity reported but contested
LD₅₀	Not established
Note	Historically implicated in necrotic bites, but recent reviews (Vetter 2008, Foradori 2005) find limited evidence for true necrosis from C. inclusum.

Bite symptoms & first aid

Symptoms

Sharp, immediate pain (often the only spider bite the victim feels at the moment of bite)
Local redness and swelling lasting 1–10 days
Necrotic lesions reported historically but not consistently confirmed in controlled studies

Commonly confused with

Brown recluse
Long-legged sac spider
Wolf spider (small specimens)

Key facts

Yellow sac spiders have been documented chewing on vehicle fuel-vapor lines, leading to fuel system failures - a Mazda recall in 2014 was attributed to this behavior. [1]

Sources

[1]Yellow Sac Spider - Penn State Extension. Accessed 2026-06-14.
[2]Vetter, R. (2008). Spiders of the genus Cheiracanthium - Journal of Medical Entomology. Accessed 2026-06-14.