Spiders that show up in a Boise attic usually didn’t start there. They follow the insects that slip in through gable vents, gaps around pipes and wiring, and loose soffit panels, then settle into a space that is quiet, dark and rarely disturbed. Once they find enough to eat, webs and egg sacs build up along the rafters and around stored boxes.
The good news is that attics are one of the easier parts of a home to defend. Most of the work comes down to cutting off the way in, removing hiding spots and checking the space a few times a year. Here’s how to do it.
Spiders You’re Likely to Find in a Boise Attic
A handful of species account for most attic sightings in the Treasure Valley:
- Cellar spiders. Long, thin legs and small bodies. They build loose, messy webs in corners and near vents.
- Common house spiders. Small brown or gray spiders that build tangled cobwebs along rafters and in stored items.
- Funnel weavers, including hobo and giant house spiders. Brown spiders that build flat sheet webs ending in a funnel, often along the edges of insulation.
- Black widows. Glossy black with a red hourglass under the abdomen. They prefer undisturbed corners and are worth handling with care.
Our spider identification guide has photos and details to help you tell them apart. If you’re finding spiders down in the insulation itself, see our post on spiders found in attic insulation.
Why Attics Attract Spiders
- Prey. Small insects come in through vents and gaps, and other bugs shelter in insulation. Our post on insulation bugs in Boise roof cavities covers the usual suspects.
- Shelter. Rafters, trusses, boxes and seasonal decorations give spiders plenty of protected corners.
- Little disturbance. Most people visit the attic a few times a year at most, so webs and egg sacs go unnoticed.
- Stable conditions. In fall, attics stay warmer than the outdoors, which draws spiders and their prey inside as Boise nights cool off.
Signs of Spiders in Your Attic
- Webs along rafters, around vents and in the corners where the roof meets the floor joists
- Round or teardrop-shaped egg sacs tucked into corners or on stored items
- Shed skins and dead insects collected in webs
- More spiders than usual in upstairs rooms, closets and around the attic hatch
Step 1: Seal the Ways In
Sealing entry points does more than any spray to keep spiders and their prey out of the attic. Check these spots with a flashlight on a bright day, when daylight coming through gaps is easy to see:
- Gable and soffit vents. Replace torn or loose screens with fine metal mesh.
- Roof penetrations. Seal gaps around plumbing vents, exhaust fans and electrical lines with caulk or foam.
- Eaves and fascia. Repair loose soffit panels and gaps where the roofline meets the siding.
- The attic hatch. Add weatherstripping around the hatch or pull-down stairs so spiders can’t move between the attic and living space.
Sealing these gaps also keeps out mice and fall invaders like boxelder bugs, which often use the same openings.
Step 2: Remove Hiding Spots
- Store items in sealed plastic bins instead of cardboard boxes, which spiders and insects can hide in and chew through.
- Keep stored items off the floor and away from the eaves so you can see the edges of the attic.
- Vacuum webs and egg sacs with a HEPA vacuum, then empty it outside.
- Replace insulation that is damp, compressed or soiled. Damp insulation draws the insects spiders feed on.
Step 3: Cut Down on Prey
Fewer insects means fewer spiders. Outdoor lights near the eaves attract insects at night, so switching to yellow or warm-toned bulbs, or using motion sensors, helps. Trim tree branches and shrubs back from the roof and siding, and keep gutters clean so moisture doesn’t collect along the roofline.
Step 4: Check the Attic Each Season
A quick look in spring and fall catches problems early. Bring a flashlight, wear gloves and long sleeves, and check vents, corners and stored items. Sticky traps placed near the hatch and along walls can show you whether activity is going up or down between checks.
Spring, Summer and Fall in Boise
Spider activity climbs through spring and summer as insects multiply. Late summer and early fall are when many people notice the most spiders, including males wandering in search of mates. As temperatures drop, spiders and other pests look for sheltered spots, so fall is the time to finish sealing the attic before winter.
When to Call a Professional
Consider professional help if you keep finding black widows, if webs and egg sacs return soon after cleaning, or if the attic is hard to move around in safely. A technician can find entry points you may not see, treat cracks and voids where spiders hide and treat the exterior where spiders enter.
Spiders are part of our residential pest control, which also covers 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 in Boise.
University of Idaho Extension’s home and garden resources are a good place to read more about common Idaho pests.
Get Help With Attic Spiders
ProGuard is based in Eagle and serves homes and businesses in Boise, Meridian, Nampa, Caldwell, Star, Middleton, Emmett and Garden City. Call (208) 352-2062 or contact us to schedule an inspection and a spider control plan for your attic.