Is the yellow sac spider dangerous?

The yellow sac spider is capable of a bite that stings briefly, but not dangerous. Bites sting and can produce a red, itchy welt that occasionally blisters, healing within a week or so. For years these were blamed for necrotic wounds, but controlled studies have not supported that. Not a medical emergency.

How do you identify a yellow sac spider?

Pale creamy yellow body with distinctly dark mouthparts, which look like a small dark mask. Longest pair of legs at the front, held forward while walking.

Where do yellow sac spiders live?

The yellow sac spider is found across most of the United States, in habitats including indoors, garden and bathroom.

Yellow Sac Spider

Stings only

Cheiracanthium inclusum · also called black-footed spider, agrarian sac spider

The yellow sac spider is the small pale spider that turns up on ceilings and walls at night, and it accounts for a large share of genuine indoor spider bites in North America — not because it is dangerous, but because it wanders over people while they sleep and bites defensively when trapped against skin.

Bite risk: Bites sting and can produce a red, itchy welt that occasionally blisters, healing within a week or so. For years these were blamed for necrotic wounds, but controlled studies have not supported that. Not a medical emergency.
Size: Body 5–10 mm. Body about a grain of rice, legs modest.
Appearance: Pale yellow, cream or faintly greenish, with conspicuously darker brown mouthparts and often dark feet. The front pair of legs is noticeably longer than the rest.
Web: Spins a small silk sleeping tube in a corner where the wall meets the ceiling, or in a folded leaf. Not a catching web.
Found in: indoors, garden, bathroom
Family: Cheiracanthiidae
Range: Most of the United States

How to identify a yellow sac spider

Pale creamy yellow body with distinctly dark mouthparts, which look like a small dark mask.
Longest pair of legs at the front, held forward while walking.
Small silk sleeping sac where a wall meets the ceiling.
Active on walls and ceilings after dark.

How it behaves

Nocturnal hunter that abandons its retreat at night to patrol walls. Does not build a catching web.

What the yellow sac spider is confused with

One observation settles each of these.

Brown recluse →

Recluses are uniformly brown with a violin mark and six eyes. Sac spiders are pale yellow with dark mouthparts and eight eyes.

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.

Not sure it was a yellow sac spider? Identify it step by step →