Sac Spider
Reviewed by TJ Jackson, Certified ACE · Updated 2026-07-24
Cheiracanthium spp. | Category: Spiders | ✓ Covered: All Seasons Pest Plan
Most people never notice a sac spider until they spot the small silk tube where the wall meets the ceiling. They’re one of the most common indoor spiders in Oregon and Washington, and one of the least recognized — small, pale, and easy to overlook. They don’t build capture webs. They hunt at night. And they’re responsible for more indoor spider bites than almost any other PNW species, though the bite itself is far less serious than their reputation suggests.
What You Need To Know About Sac Spiders
Our ACE Certified Technician TJ breaks down sac spiders — how to spot the silk retreat, what a bite actually does, and how to keep them out.
Frequently Asked Questions
What does a sac spider look like?
Small and pale — cream, light yellow, or faintly green, about 1/4″ to 3/8″ with slightly darker mouthparts and no visible markings. The easiest tell isn’t the spider at all: it’s the small silk tube retreat where the wall meets the ceiling.
Do sac spiders build webs?
Not for catching prey. They hunt on foot at night. The only silk they produce is the tube-shaped sac they rest in during the day — which is where the name comes from. A silk tube with no capture web attached is a sac spider retreat.
Are sac spider bites dangerous?
No. Sac spiders were blamed for years for necrotic wounds, but current research doesn’t support it. Verified bites cause mild local stinging, redness, and sometimes slight swelling that clears in a few days. The only PNW spider with real medical risk is the black widow.
Why do sac spiders bite more than other spiders?
Behavior, not aggression. They wander at night to hunt, which means they’re more likely than web-bound spiders to end up in bedding, clothing, or a towel. Nearly every sac spider bite happens when the spider gets pressed against skin. They don’t seek people out.
Does the All Seasons Pest Plan cover sac spiders?
Yes — including treatment of active infestations, exterior web and retreat removal, and free re-service visits if activity returns between scheduled treatments.
Quick Answer: Sac spiders (Cheiracanthium spp.) are small, pale cream or yellowish spiders about 1/4″ to 3/8″ long that are among the most common indoor spiders in Oregon and Washington. They don’t build capture webs — they hunt at night and rest during the day in a small silk tube retreat, usually at a wall-ceiling joint or behind a baseboard. That silk tube is the fastest way to identify them. Bites are more common than with other PNW spiders simply because sac spiders wander into bedding and clothing, but the bite itself is mild: local stinging and redness that resolves in a few days.
Most important distinction: The necrotic-wound reputation is outdated. Sac spiders are not medically significant. The only PNW spider that poses a real medical risk is the black widow.
Behavior & Biology
Sac spiders belong to the genus Cheiracanthium, a group of small hunting spiders found throughout North America. In the Pacific Northwest they’re present year-round but become noticeably more common indoors from late summer through fall, when cooling temperatures push them in from gardens, leaf litter, and exterior siding.
Unlike orb weavers or cellar spiders, sac spiders build no capture web. They’re ambush and pursuit hunters that leave their retreat after dark and range across walls, ceilings, and floors looking for small insects, insect eggs, and occasionally other spiders. Their pale coloring and small size make them easy to miss against a light-painted wall.
The silk retreat is the giveaway. During daylight hours the spider seals itself inside a small tube-shaped sac roughly the size of a grain of rice, tucked into a corner, a wall-ceiling seam, a curtain fold, or the underside of a shelf. Female sac spiders also use these retreats to guard their egg sacs, which is why you may find several clustered in the same area.
Sac spiders account for a disproportionate share of verified indoor spider bites in the PNW, but that’s a function of proximity rather than temperament. Because they wander at night, they end up in bedsheets, folded laundry, and shoes far more often than spiders that stay put in a web. A bite happens when the spider is trapped against skin and has nowhere to go.
Local context: Oregon and Washington
Sac spiders are the one spider that ignores our calendar
Across five years of spider service records in Portland, Vancouver, Salem, Olympia and Kelso, our spider calls peak in September at 17.1% of the year. Our records tag spiders as a group rather than by species, so the orange line is every spider we treat.
Sac spiders break the pattern. Of 1,847 sightings logged in Oregon and Washington between 2021 and 2025, the peak is May at 16.8%, with April and June close behind. Sightings then fall through the exact weeks when the rest of the spider season is ramping up. Line the two series up and they barely agree, the weakest match of the five spiders on our pages.
Both curves are true, and they describe different things. Spring is when sac spiders are out on plants and fences where people notice and photograph them. The complaints that reach us are about the small silk retreats in ceiling corners and window frames indoors, which is a slower, quieter problem that surfaces once people are inside more.
Sightings peak in spring, spider calls peak in fall
Each series is its share of the annual total, so the two are directly comparable. The orange line is all spider calls; our records do not break out species.
Blue line: spider sightings the public logged in Oregon and Washington, 2021 to 2025. See the records on iNaturalist.
Two different calendars
Sightings measure what people run into outdoors. Our service records measure what makes them pick up the phone. For most spiders the two rise together. For sac spiders they do not, which is a fair warning that a spring sighting on the patio and a silk sac in your window corner in November are not the same problem.
What to do in each season
In spring, a sac spider on a fence or a shrub is doing its job and needs nothing from you. In fall and winter, the small silk retreats in ceiling corners, behind pictures and along window frames are the ones worth wiping out, because that is where the indoor population overwinters.
Sac spiders are among the few PNW spiders capable of a painful bite, though documented bites here are rare. Vacuum rather than squash, and keep the treatment focused on the interior edges where the retreats show up.
When each spider’s season actually lands
One row per spider, twelve months of Google search interest in Oregon and Washington, 2021 to 2025, with August, September and October banded. Our own spider calls are the bottom row.
Each row is one spider’s year, darkest in its busiest month. The right column is how much of that spider’s year lands in the three banded months. See these five terms in Google Trends. Sac spider searches are rare enough that this row jumps around, which is why the chart above it uses sightings instead.
“Sac spiders are the ones I find during winter inspections, tucked into little silk sacs in ceiling corners and window frames, not the ones people call about in September. They can give you a bite that stings, but that is uncommon here. Wipe the sacs out when you see them, vacuum instead of crushing, and if they keep coming back we treat the interior edges and the window channels rather than hosing down the yard.”TJ Jackson · ACE, Director of Operations, Interstate Pest Management
Free re-service if they come back between scheduled visits. Sac spiders are covered under the All Seasons Pest Plan from $39/month: interior and exterior treatments. QualityPro certified.
Book an interior spider service
- Portland503-782-1899
- Vancouver360-996-1442
- Salem503-461-0259
- Olympia360-525-8004
- Kelso / Longview360-515-3882
Sources: Interstate Pest Management service records, 2021 to 2025, new customers only, all spider species combined. Sightings: public iNaturalist records for Oregon and Washington, 2021 to 2025, counted by the month each spider was seen. Species notes: Pacific Northwest Pest Management Handbooks and Oregon Department of Agriculture, Oregon Spiders: Facts and Fiction. Sac spider searches in Oregon and Washington are too rare to chart month by month. Updated September 2026.
What To Do If You Have Sac Spiders
Sac spiders are manageable with a few straightforward habits. The goal is removing their retreats and cutting off the insect supply that keeps them around.
Vacuum the silk retreats
Run a vacuum along wall-ceiling joints, corners, and behind furniture. This removes both the spiders and any egg sacs in one pass. Empty the canister outside afterward.
Reduce their food source
Sac spiders follow insects. Cutting down interior gnats, flies, and other small insects removes the reason they stay. Exterior lighting changes help too, since lights draw prey to the house.
Shake out bedding and clothing
Nearly every sac spider bite happens when one gets trapped against skin. Shaking out laundry left on the floor and keeping bedding off the ground eliminates most of that risk.
Seal entry points
Window screens, door sweeps, and gaps around siding and utility penetrations are the main routes in. Sealing these reduces sac spiders along with everything else that wanders inside in fall.
Plans That Cover All PNW Spider Species
All Seasons Pest Plan
$39/month
Setup fee ~$260 for initial treatment
Year-round protection from the pests Pacific Northwest homeowners deal with most — spiders, ants, wasps, box elder bugs, and more. Includes exterior web removal with every visit.
- Recurring exterior treatments
- Exterior web removal
- Free re-service between visits
Pest & Rodent Bundle
$47/month
Setup fee ~$280 for initial treatment
The most complete protection for your home. Full pest coverage plus active rodent monitoring — one plan, one team, one less thing to worry about.
- Everything in Pest & Rodent plans
- Best value for whole-home protection
- Free re-service guarantee