As summer fades in the Treasure Valley and cooler evenings set in, many homeowners notice an unsettling trend—more spiders appearing inside their homes. From garages to basements, and even tucked away in bathrooms or kitchens, spiders seem to arrive in waves just as families are settling into the fall season. While it might feel like your home is suddenly being invaded, there are very real biological and seasonal reasons for this behavior.
Why Spiders Become More Noticeable in Late Summer and Fall
Spiders are present year-round, but they become more visible as the weather shifts. In the Treasure Valley, warm days followed by cooler nights trigger both prey activity and spider movement. Late summer is also the peak of spider mating season. Male spiders, in particular, wander farther from their hidden webs to search for females. This is why you suddenly spot them along walls, in corners, and near baseboards.
Another factor is temperature. As outdoor conditions cool, spiders follow prey indoors where food sources—such as ants, flies, and other insects—remain active. Homes provide stable shelter, warmth, and protection from sudden temperature drops that can threaten spider survival.
Common Spiders in Southwest Idaho Homes
- Hobo spiders – Brown, fast-moving, and often confused with brown recluse (which are not established in Idaho). They build funnel webs near foundations and sometimes indoors.
Black widow spiders – Glossy black with a red hourglass marking; they prefer dark, undisturbed areas like garages, crawl spaces, and sheds.
Cellar spiders (daddy longlegs) – Harmless, but known for their long legs and messy webs in basements and corners.
Orb weavers – Large, round-abdomen spiders that build distinctive webs outdoors but may move closer to structures when nights turn cold.
Understanding which species you’re dealing with helps determine whether the issue is primarily nuisance or a potential health concern.
Why Spiders Choose the Indoors
Spiders aren’t typically seeking humans—they’re chasing food. Lights on porches and around windows attract flying insects, which in turn lure spiders. Once inside, they settle in dark, quiet areas like attics, basements, and behind furniture. The abundance of prey in these locations encourages them to stay and breed.
What Homeowners Can Do
If you’re seeing more spiders this time of year, there are practical steps to limit their numbers:
Reduce clutter in basements, garages, and storage areas where spiders hide.
Seal entry points around windows, doors, and foundation cracks.
Control outdoor lighting or switch to yellow bulbs that attract fewer insects.
Vacuum webs and dispose of them outside to discourage reoccupation.
Trim vegetation away from siding and foundations to reduce outdoor spider harborage.
How Professional Spider Control Works
While many spiders are harmless, finding them indoors in higher numbers can be unsettling, especially for families with children. Professional treatments go beyond simple web removal:
Perimeter sprays block spider entry around the foundation.
Targeted dust applications in wall voids, attics, and crawl spaces disrupt nesting sites.
Insect control reduces the food source that draws spiders indoors in the first place.
Follow-up services during peak spider activity months (late summer into fall) keep populations in check as weather continues to cool.
At Pestcom, we often see the heaviest spider activity from August through October in Nampa, Boise, and surrounding towns. By planning services ahead of this seasonal surge, homeowners can enjoy a spider-free fall without worrying about surprise encounters in corners or garages.
When to Call for Help
If you’re noticing multiple spiders inside over a short period—or if you’ve identified potentially dangerous species like black widows—it’s time to schedule a professional inspection. Spiders play an important role in nature, but indoors, they’re better left outside where they belong.