Spiders are a common sight in many homes. Their presence indoors is a natural part of their behavior, driven by environmental factors and biological needs. Understanding when and why spiders enter homes can help demystify their appearance and provide insight into their habits.
Seasonal Activity Indoors
Spider activity inside homes changes throughout the year. In late summer and early autumn, typically from mid-August through October, a significant increase in spider sightings occurs. This period is often linked to the mating season, when male spiders become more mobile and venture out in search of females. Male spiders, particularly house spiders, will abandon their webs and roam more widely, making them more visible as they search for a mate.
As outdoor temperatures begin to drop in the fall, many spiders seek sheltered locations to survive the colder months. While some species may enter a state of reduced activity or dormancy, others continue to be active indoors, drawn by the more stable environment. This migration can lead to an influx of spiders in basements, attics, or garages as they seek refuge from harsh conditions.
During winter, many spiders are less visible, but they do not disappear entirely. Some species may overwinter in walls or undisturbed areas within homes, with egg sacs often remaining hidden until spring. In spring, warming temperatures prompt many spider species to become more active, emerging from their dormant states and venturing out to find food and mates. This period also marks the beginning of breeding season for many species, leading to increased web building and egg-laying activity.
Why Spiders Seek Indoor Shelter
Spiders are influenced by various environmental factors that encourage them to move indoors. Changes in outdoor temperature are a primary motivation, as spiders are ectothermic, meaning their body temperature is regulated by their surroundings. When it becomes too cold or excessively hot outdoors, homes offer a more stable and favorable microclimate for their survival.
The availability of food sources also plays a role in spiders seeking indoor shelter. If insect populations decline outdoors due to colder weather, spiders may follow their prey indoors, where other insects like flies and ants may still be active. Spiders are carnivores and will enter homes to find a consistent supply of insects.
Humidity levels inside a home can also attract spiders, particularly species that prefer moist environments. Damp areas such as basements, crawl spaces, and bathrooms provide suitable conditions for spiders to maintain hydration and support their reproductive cycles. The presence of moisture can also draw in insects, which in turn attracts spiders searching for food.
Common Indoor Spider Species
Several spider species are frequently encountered inside homes, each with distinct characteristics. The American house spider (Parasteatoda tepidariorum) is one of the most common, often found spinning messy, tangled webs in corners and undisturbed areas. These spiders are typically small, brown, and generally harmless, contributing to pest control by preying on flies and mosquitoes.
Cellar spiders (Pholcus phalangioides), often recognized by their long, thin legs, prefer dark and damp locations like basements and closets. They construct loose, irregular webs and are also harmless to humans. Wolf spiders are larger, hairy, and do not build webs to catch prey; instead, they actively hunt insects on the ground. They may enter homes in search of warmth or food, particularly in the fall.
Sac spiders, often pale in color, are active hunters that do not rely on webs for prey capture. They spend daylight hours in silken sacs, often found in upper room corners or wall cracks, and hunt at night. Some species, like the funnel web spiders, can also be found indoors, building dense, sheet-like webs. Some spiders, such as the American house spider, live their entire lives indoors, while others are seasonal invaders seeking temporary shelter.
Where Spiders Are Found Indoors
Once inside, spiders gravitate towards specific areas that offer shelter, food, or undisturbed environments. Common hiding spots include dark, secluded corners of rooms, especially where walls meet the ceiling. These locations provide stability for their webs and protection from disturbances.
Basements, attics, and crawl spaces are popular spider habitats due to their typically higher humidity, stable temperatures, and reduced human activity. Spiders also frequently hide behind furniture, large appliances, and inside cupboards and cabinets, seeking out the narrow gaps and dark spaces these items provide. Entry points such as cracks in walls, gaps around windows and doors, or poorly sealed utility lines can also lead to spiders being found near these areas.