Photo: Anna N Chapman, CC0, via Wikimedia Commons
Kansas City Pest Identification
Cheiracanthium mildei / C. inclusumYellow Sac Spider Identification
A small pale spider that hides in a silk sac where the wall meets the ceiling and is responsible for a good share of the "mystery bites" people wake up with in Kansas City.
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How to Identify It
Pale yellow, cream, or light green with a slightly darker stripe down the abdomen and dark tips on the feet. The hiding sac is a small flat silk tent in the corner of a ceiling, behind a picture frame, or in a window track.
Size: Body 5–10 mm
Commonly Confused With
Often mistaken for a young brown recluse. Sac spiders are paler, have eight eyes in two rows, and build the telltale silk retreat.
Why It Shows Up
They come in through window screens and gaps in fall and then hunt at night along walls and ceilings. They are drawn to homes with a steady supply of small insects.
Where Homeowners Find It
Upper corners of rooms, along ceiling edges, behind curtains and pictures, in window and door tracks, and inside folded laundry or bedding.
Seasonal Activity in KC
Indoors year-round; numbers rise in late summer and fall.
Risk Level
Bites are more common than from most spiders because they hide in bedding and clothing. Reactions are usually a red, itchy welt that heals in a week; not dangerous, but unpleasant.
What You Can Do Yourself
- • Vacuum the ceiling-corner sacs and window tracks regularly.
- • Shake out bedding and laundry that has sat out.
- • Repair screens and seal window frames.
What Professional Treatment Involves
Crack-and-crevice treatment along ceiling and wall junctions and window frames, exterior treatment around windows and eaves, and reduction of the insect prey. Sac spiders respond well to a general spider program.
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Common Questions
How do I tell a yellow sac spider from something that looks similar?
Often mistaken for a young brown recluse. Sac spiders are paler, have eight eyes in two rows, and build the telltale silk retreat.
Do I need professional treatment for yellow sac spider?
Crack-and-crevice treatment along ceiling and wall junctions and window frames, exterior treatment around windows and eaves, and reduction of the insect prey. Sac spiders respond well to a general spider program.