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Be careful

Yellow sac spiders

Northern yellow sac spider

Cheiracanthium mildei
Also called yellow sac spider, long-legged sac spider, European yellow sac spider

One of the house spiders most likely to bite, usually when trapped in clothes or bedding; the bite stings and reddens but is rarely serious.

Northern yellow sac spider, photo 1
Photo: Alexis Tinker-Tsavalas, CC BY 4.0, via iNaturalist
SizeBody about 5–10 mm (about 1/4 to 3/8 inch)
Where in the houseBedroom, living room, windows and walls, bathroom, kitchen, closets
WhenMost noticed late summer through fall, but found indoors year-round.

Check these features

  1. Pale yellow, cream or greenish abdomen, sometimes with a faint darker stripe down the middle
  2. Front body and legs slightly darker than the abdomen; dark tips on the jaws and feet
  3. First pair of legs noticeably longer than the others
  4. No web; rests by day in a small, white silk sac in a wall or ceiling corner, behind pictures or on shelves
  5. Runs quickly across walls and ceilings at night and drops on a silk line when disturbed

Bites and stings

Bites usually happen when the spider gets trapped against skin in clothing or bedding. A bite causes an immediate sharp sting, then redness and mild swelling, sometimes itching; it typically fades within days. There is no good evidence these spiders cause spreading dead-skin wounds. Get medical care for signs of infection (spreading redness, warmth, pus, fever), a sore that keeps growing, or any sign of allergic reaction such as trouble breathing or swelling of the face.

What to do

  1. Wash the bite with soap and water and apply a cool, damp cloth or wrapped ice.
  2. Keep the area clean and watch it for a few days.
  3. Call 911 for trouble breathing or swelling of the face or throat.
  4. See a doctor if the area becomes hot, more painful, oozes, keeps growing, or you develop a fever.
  5. If you can, catch the spider in a jar for identification.

Look-alikes

Agrarian sac spider (Cheiracanthium inclusum)Almost identical; it is native and lives mostly outdoors in gardens and fields, while C. mildei is mainly found indoors. An expert is needed to separate them.
Broad-faced sac spider (Trachelas tranquillus)Has a dark, glossy reddish-brown front body and a dull grayish-tan abdomen, not an all-pale body.
Ghost spiders (Anyphaenidae)Also pale and night-active but usually show darker markings on the abdomen.

Why it came inside

This European spider is mainly an indoor species that hunts small insects at night, and outdoor sac spiders also move into homes and cars in late summer and fall to spend the winter.

Keep it out

  • Shake out clothing, towels and bedding that have been on the floor or left unused.
  • Vacuum silk sacs from ceiling corners, behind furniture and around window frames.
  • Fit door sweeps and tight window screens, and keep windows closed or screened at night.
  • Seal cracks around windows, doors and wall penetrations and reduce clutter.

What helps

Links go to Amazon search results so you can compare current options. As an Amazon Associate I earn from qualifying purchases. Always follow the product label.

Vacuum with a hose

Lets you remove bugs, webs and egg sacs without touching them. Empty the bag or canister outside right away.

See options on Amazon
Screen repair kit

Patches or replaces torn window and door screens, one of the most common ways insects get in.

See options on Amazon
Door sweep

Closes the gap under an exterior door. If you can see daylight under the door, bugs can get in.

See options on Amazon
Caulk and sealant

Silicone or siliconized acrylic caulk closes cracks around windows, pipes and baseboards. Bigger gaps need foam backer rod or expanding foam first.

See options on Amazon
Weatherstripping

Seals the gaps around doors and windows that let in drafts and bugs alike.

See options on Amazon
Sticky traps

Flat glue traps set along walls and in corners show what is moving through and where. Place them where pets and children can't reach.

See options on Amazon
Bug catcher

A long-handled catcher moves a spider or insect outside without you having to touch it.

See options on Amazon

Sources

  1. Bohart Museum of Entomology, UC Davis
  2. Vetter et al. 2006, Am. J. Trop. Med. Hyg. (Duke Scholars record)
  3. Burke Museum, University of Washington
  4. Washington State Department of Health
  5. University of Minnesota Extension
  6. Utah State University Extension
  7. University of Arkansas Arthropod Museum

Checked October 18, 2026. Rating backed by 4 sources. How we rate danger.

Be careful

Agrarian sac spider

Cheiracanthium inclusum
Also called yellow sac spider, black-footed yellow sac spider

A bite stings and can redden, itch or blister for a few days, but it is rarely serious.

Agrarian sac spider, photo 1
Photo: Jhonatan Matheus, CC BY 4.0, via iNaturalist
SizeBody about 5–10 mm (about 1/4 to 3/8 inch); about 3/4 inch with legs spread
Where in the houseOutside near the house, windows and walls, bedroom, living room, garage
WhenAdults are active outdoors from about April through November; indoors it is seen most in late summer and fall.

Check these features

  1. Pale yellowish, cream or grayish-tan body without obvious markings
  2. Front body slightly darker than the abdomen; dark tips on the feet and jaws
  3. Long, thin legs without obvious spines, with the front pair the longest
  4. No catching web; hides by day in a small silk sac in a rolled leaf, under bark or in a corner
  5. Hunts at night on plants, walls and ceilings

Bites and stings

Most bites happen during gardening or yard work, or when a spider is trapped in clothing. A bite hurts right away and can cause redness, swelling, itching and burning for up to an hour or more, sometimes a blister; some people feel mildly unwell. Redness usually fades in a few days and the skin heals in one to two weeks. Get medical care for spreading redness, warmth, pus or fever, a sore that keeps growing, or any sign of allergic reaction such as trouble breathing or swelling of the face.

What to do

  1. Wash the bite with soap and water and apply a cool, damp cloth or wrapped ice.
  2. Keep it clean and watch it over the next few days.
  3. Call 911 for trouble breathing or swelling of the face or throat.
  4. See a doctor if the area becomes hot, very painful, oozes, keeps growing, or you develop a fever.
  5. If you can, catch the spider in a jar for identification.

Look-alikes

Northern yellow sac spider (Cheiracanthium mildei)Nearly identical but mostly found indoors; experts separate them by microscopic features.
Broad-faced sac spider (Trachelas tranquillus)Has a shiny dark reddish-brown front body that contrasts with a dull pale abdomen.
Ghost spiders (Anyphaenidae)Also pale and active at night but usually with darker abdominal markings.

Why it came inside

A native garden and field spider that occasionally wanders indoors, and young spiders move into buildings and cars in late summer and fall to overwinter in silk sacs.

Keep it out

  • Wear gloves when gardening, pruning or handling stored outdoor items.
  • Shake out gloves, clothing and towels left outdoors or on the floor.
  • Fit door sweeps and tight window screens, and seal gaps around windows and doors.
  • Vacuum silk sacs from corners and along window frames.

What helps

Links go to Amazon search results so you can compare current options. As an Amazon Associate I earn from qualifying purchases. Always follow the product label.

Vacuum with a hose

Lets you remove bugs, webs and egg sacs without touching them. Empty the bag or canister outside right away.

See options on Amazon
Screen repair kit

Patches or replaces torn window and door screens, one of the most common ways insects get in.

See options on Amazon
Door sweep

Closes the gap under an exterior door. If you can see daylight under the door, bugs can get in.

See options on Amazon
Caulk and sealant

Silicone or siliconized acrylic caulk closes cracks around windows, pipes and baseboards. Bigger gaps need foam backer rod or expanding foam first.

See options on Amazon
Weatherstripping

Seals the gaps around doors and windows that let in drafts and bugs alike.

See options on Amazon
Sticky traps

Flat glue traps set along walls and in corners show what is moving through and where. Place them where pets and children can't reach.

See options on Amazon
Bug catcher

A long-handled catcher moves a spider or insect outside without you having to touch it.

See options on Amazon

Sources

  1. University of Arkansas Arthropod Museum
  2. Bohart Museum of Entomology, UC Davis
  3. New Mexico State University
  4. Vetter et al. 2006, Am. J. Trop. Med. Hyg. (Duke Scholars record)
  5. Utah State University Extension

Checked October 18, 2026. Rating backed by 4 sources. How we rate danger.