Why do I have spiders in my finished basement?

It’s not uncommon to find spiders in basements, even finished ones. Spiders are adept at finding their way into buildings and establishing webs in undisturbed corners. While you may not enjoy having 8-legged roommates, their presence doesn’t necessarily indicate a problem. Understanding why spiders end up in basements can help you take sensible steps to reduce their numbers if desired.

Why Spiders Love Basements

Several factors make basements an attractive habitat for spiders:

1. Cool, Damp Conditions

Spiders prefer cooler, damper environments. Basements tend to maintain temperatures 10-15°F lower than the rest of the home. Concrete foundation walls also readily absorb moisture from the soil. This cooler, damper environment suits spiders well.

2. Cracks and Crevices

Even the most carefully finished basement has small gaps and openings in the walls where utilities and pipes run. Spiders exploit these cracks to gain entry from the outside. Undisturbed corners, ceiling joists, and wall voids provide ideal web-spinning locations once inside.

3. Prey

Basements contain plentiful prey for spiders such as insects and other arthropods. Silverfish, crickets, centipedes, pill bugs, and ants may find their way inside, providing a convenient food source. Spiders take advantage of this abundance.

4. Few Disturbances

Compared to inhabited areas of a home, basements experience minimal human activity. With few disturbances, spiders can construct sturdy webs and remain undisturbed for long periods.

Common Basement Spider Species

Many spider species may inhabit basements, but some of the most common include:

Cellar Spiders

Cellar spiders produce messy, tangled webs in corners or ceiling joists. Despite their name, they can inhabit any cool, sheltered part of a structure. They have long, spindly legs and small bodies, but are not dangerous.

American House Spiders

American house spiders have a distinct “violin” pattern on their backs. They construct messy webs in undisturbed corners and prey on other insects. House spiders have potent venom but are reluctant to bite humans.

Grass Spiders

Grass spiders often wander inside in search of mates. They build funnel-shaped webs in corners or windows to capture prey. Most grass spiders have striped legs and grow up to 15mm in body length. Their venom is not medically significant.

Are Cellar Spiders Dangerous?

Of the common basement spider species, none pose a serious danger to humans. The venomous spiders found in North America like black widows and brown recluses prefer warm, dry locations and rarely inhabit basements.

Cellar spiders in particular have very mild venom that is not harmful except in rare cases of allergic reaction. Their small fangs also cannot easily penetrate human skin. Despite their unsettling appearance, cellar spiders are essentially harmless.

Will Spiders Infest My Basement?

While individual spiders certainly may take up residence, true spider “infestations” are uncommon. Spiders are territorial and will fight or cannibalize each other when forced into close proximity. This limits their numbers relative to the available space.

Seeing 5-10 spiders over an entire basement is reasonable given the favorable habitat. Significantly higher numbers likely indicate an excessive prey source drawing in large amounts of spiders. This may warrant investigating and eliminating conditions that allow insects to breed.

Steps to Reduce Basement Spiders

If desired, you can take proactive steps to reduce spider populations in your basement:

Remove Clutter and Debris

Clearing boxes, papers, and general clutter deprives spiders of web attachment points and hiding spots. Periodic cleaning also disturbs established webs.

Turn Lights On

Spiders avoid well-lit areas. Leave basement lights on or install additional lighting to make the environment less hospitable.

Fill in Cracks

Caulk and seal any cracks in the foundation and around windows, utilities, and doors to block spider entry points.

Modify Environmental Conditions

Use dehumidifiers to keep relative humidity under 50% and avoid excessive moisture. Increase ventilation. Raise temperatures to around 65°F if feasible.

Use Repellents

Apply insecticidal dusts containing silica gel in window frames, wall voids, or anywhere spiders may enter. These provide a dry barrier spiders avoid.

Remove Prey Sources

Eliminate any moist wood, compost piles, or clutter where insects breed. Fix any leaky plumbing. traps for crickets, cockroaches, or other common spider prey.

Employ Natural Predators

Certain insects like house centipedes feed on spiders. Avoid killing these beneficial predators if control is desired.

When to Call an Exterminator

Most basement spider issues can be self-managed. Contact a pest control professional if you observe:

– Bites or skin irritation indicating dangerous species like widows or recluses

– Large numbers of spiders well above normal

– Repeated infestations every season

– Allergic reactions to spiders

– Spiders in living areas above the basement

Otherwise, vigilant cleaning, sealing cracks, and modifying the environment should help curb populations.

Coexisting with Basement Spiders

For most homeowners, the presence of some spiders in the basement is inevitable. Practicing tolerance and coexistence is preferable to constant eradication efforts. Despite their unsettling look, most species found in Minnesota homes are harmless.

With proper identification and basic precautions, there is no need to fear basement spiders. Their presence can even be beneficial, as many species prey on insects considered nuisance pests. Unless populations are truly excessive, the best solution may be to simply leave these unusual basement roommates be.

Frequently Asked Questions

What are the most common spiders found in basements?

Cellar spiders, American house spiders, and grass spiders are most frequently encountered in Minnesota basements. Other common species include cobweb spiders and funnel weavers.

How do spiders get in my basement?

Spiders enter through small cracks in the foundation, gaps around windows or doors, openings for utilities, and any other crevices that lead from the outside to inside.

Will I get spiders if I finish my basement?

Yes, finishing a basement does not prevent spiders. They are adept at finding small gaps in walls, ceilings, and floors. Proper sealing during finishing may reduce entry points.

Are wolf spiders common in basements?

Wolf spiders prefer outdoor habitats and are less common than web-spinning species inside. However, they occasionally wander indoors and may be seen in basements on occasion.

What temperature do basement spiders prefer?

Most species prefer cooler temperatures between 45-75°F. Heating a basement to around 65°F can discourage spiders who prefer cooler conditions.

Can I use insecticides to control basement spiders?

Insecticide sprays and foggers are not very effective against spiders. Applying insecticidal dusts in cracks and voids or removing prey sources are better approaches.

Will a dehumidifier get rid of basement spiders?

A dehumidifier can make a basement less attractive by reducing favorable damp conditions. However, spiders may persist in corners or areas unaffected by the dehumidifier.

Are daddy long legs spiders?

Despite their name, daddy long legs are actually not true spiders. They belong to a different order of arachnids called harvestmen and lack characteristics like silk-producing spinnerets.

How do I seal cracks to prevent basement spider entry?

Use caulk, expandable foam filler, weatherstripping, or other sealants to close cracks around windows, doors, pipes, wiring holes, and the foundation. Pay special attention to corners and ceilings.

Why do I see more spiders in my basement in warmer months?

Late summer and early fall is prime mating and hunting time when spider populations peak. Cooler basement temperatures also become more favorable to spiders as outside temperatures rise.