Pull back a section of attic insulation in a Star home and you may find more than dust: webs, egg sacs, shed skins and the spiders themselves. Insulation gives spiders a dark, protected place to hide, and the insects that wander into attics give them plenty to eat. Most of these spiders are harmless, but a few are worth identifying before you reach in with bare hands.
Here’s which spiders are most likely to be in your attic insulation, how to tell them apart and how to keep them from settling in.
Why Spiders Live in Attic Insulation
- Shelter. Loose fill and batts are full of small spaces that protect spiders and their egg sacs.
- Food. Small insects come in through vents and gaps, and some insects live in the insulation itself. Our post on insulation bugs in roof cavities covers what else turns up there.
- Little disturbance. Most people go into the attic only a few times a year.
- Warmth. As fall nights cool off, attics stay warmer than the outdoors.
Spiders Commonly Found in Attic Insulation
Funnel weavers (hobo and giant house spiders)
Brown spiders with patterned abdomens that build flat sheet webs ending in a funnel, often right along the edge of insulation or under the lip of a batt. Hobo spiders once had a reputation for dangerous bites, but later research hasn’t supported it. The Idaho hobo spider bulletin explains how to identify them.
Cellar spiders
Small bodies with very long, thin legs. They build loose, irregular webs in corners, around vents and over insulation, and they prey on other spiders.
Common house spiders
Small brown or gray spiders that build tangled cobwebs in rafters and corners and on stored items.
Wolf spiders
Large, hairy, brown and fast. They hunt on the ground instead of using webs, and they occasionally wander into attics along with their prey.
Black widows
Glossy black with a red hourglass on the underside. They build messy, strong webs in quiet corners and along the edges of insulation. Their bite is venomous, so wear gloves and long sleeves when working near insulation.
Brown recluse spiders are often suspected, but they’re not established in Idaho. Most spiders mistaken for them are other brown spiders. Our spider identification guide has photos to help.
How to Tell What You Have
- Web shape. Sheet webs with a funnel point to funnel weavers. Loose, irregular webs suggest cellar or house spiders. Strong, messy webs low in corners may be black widows. No web at all suggests a hunting spider like a wolf spider.
- Body and legs. Very long, thin legs mean cellar spiders. A shiny black body with a red mark means black widow.
- Egg sacs. Round, papery sacs in corners and webs mean spiders are breeding in the attic, not just passing through.
Health and Comfort Concerns
Most attic spiders are shy and bite only when pressed against skin. The bigger concerns are black widows and the debris that builds up: webs, shed skins and dead insects in insulation can stir up dust when disturbed. Wear gloves, long sleeves and a dust mask when working in insulation.
Prevention Steps
- Seal entry points. Repair vent screens, seal gaps around roof penetrations and wiring, and weatherstrip the attic hatch.
- Control moisture. Fix roof leaks and make sure bathroom and kitchen fans vent outside, not into the attic. Damp insulation attracts the insects spiders eat.
- Replace damaged insulation. Insulation that is wet, compressed or soiled should be replaced.
- Store items in sealed bins and keep them off the attic floor where possible.
- Check twice a year, in spring and fall, and vacuum webs and egg sacs with a HEPA vacuum.
Our post on how to keep spiders out of attics goes step by step through sealing and cleanup.
When to Call a Professional
Call for help if you’re finding black widows, if webs and egg sacs keep returning after cleanup or if spiders are moving from the attic into living spaces. A technician can find entry points, treat cracks and voids where spiders hide and treat the exterior where they come in.
Spiders are part of our residential pest control, along with ants, wasps and hornets, mice, rats and fall invaders. We offer quarterly, bi-annual and one-time service. Quarterly service plan customers get free return visits. No contracts; cancel with 30 days’ notice. Rodent service is included at no extra cost with quarterly service plans; traps and materials are billed separately. We also serve commercial properties.
Attic Spider FAQs
Why do I see more spiders in the fall?
Many spiders mature in late summer, and males wander looking for mates. Cooler nights also push insects, and the spiders that hunt them, toward the shelter of attics and wall voids.
Should I replace insulation that has spiders in it?
Usually not just because of spiders. Removing webs, sealing entry points and reducing the insects they feed on is normally enough.
Spiders in Your Star Attic?
ProGuard is based in Eagle and serves homes and businesses in Star, Boise, Meridian, Nampa, Caldwell, Middleton, Emmett and Garden City. Call (208) 352-2062 or contact us to schedule an inspection.