# Yellow Sac Spider — Spider Squad

## Common Name
Yellow sac spider

## Scientific Name
Cheiracanthium mildei and Cheiracanthium inclusum (both found in Ontario)

## Size
Small. Body: 5 to 10 mm.

## Appearance
Pale yellow, cream, or light green in colour. Uniform in colour without strong markings. The abdomen may have a faint dark line along the dorsal surface. Legs are slightly darker than the body. Often described as "small and pale" or "almost translucent looking."

## Behaviour and Web
Yellow sac spiders do not build capture webs. They build a silk tube retreat — a flattened, tube-shaped silk sac — in sheltered locations: behind window trim, under bark, in rolled leaves, behind picture frames, along ceiling-wall junctions, and in any tight, protected crevice. This retreat is where they rest during the day.

At night they are active hunters, foraging for small insects.

## Where Found in Homes
- Along ceiling-wall junctions (they run along this junction at night)
- Behind trim, particularly around windows and doors
- Under furniture
- In rolled or bundled materials in storage areas
- Garages and basements

They are more commonly found indoors than most Ontario spider species because they seek protected, enclosed retreats inside structures.

## Seasonal Pattern
Active year-round in heated spaces. Most noticeable in late summer and fall when they move indoors seeking warmth and shelter. Outdoor populations migrate inside as temperatures drop in September and October.

## Bite Risk
Yellow sac spiders are the most clinically significant spider for bites among common Ontario species — but the risk is still low. They are more likely to bite than most spiders because their roaming behaviour brings them into contact with humans at night and in clothing, bedding, and shoes left on the floor.

Bite reaction: local pain, redness, and swelling. Some individuals develop a necrotic (tissue-damaging) reaction, though this is uncommon. Yellow sac spider bites have historically been blamed for necrotic wounds in North America, though many such diagnoses are disputed and wounds attributed to other causes. If a bite causes expanding redness, warmth, or tissue breakdown beyond 24 to 48 hours, seek medical attention.

They are not aggressive — they bite only when trapped against skin.

## Professional Treatment
Interior spot treatment is effective for yellow sac spider infestations because they concentrate in specific retreats. If you're finding silk tube retreats behind trim or along ceiling junctions, let your Spider Squad operator know — targeted interior treatment of these zones is more effective than exterior perimeter treatment alone for established indoor populations.

For information on bites: spidersquad.ca/spider-bites/