The family Pholcidae, commonly known as cellar spiders, are arachnids found throughout the world, frequently encountered inside human dwellings. These spiders have successfully adapted to a broad ecological niche, ranging from natural environments to the quiet corners of our homes. Understanding their dwelling places requires looking at both the physical locations they inhabit and the specific environmental conditions they seek.
Identification and Common Misunderstandings
Cellar spiders are distinct arachnids characterized by small, oval bodies and extremely long, thin legs. They are true spiders, possessing two body segments—a cephalothorax and an abdomen—along with venom glands and the ability to spin silk. Their webs are typically messy, irregular tangles of non-sticky silk constructed in sheltered areas. They are often confused with the Harvestman (Opiliones), which is not a true spider; Harvestmen have a single fused body segment, lack silk glands, and do not produce venom.
Preferred Indoor Habitats
As their common name suggests, cellar spiders frequently establish themselves in the lower, undisturbed areas of human structures. Preferred indoor locations include cellars, unfinished basements, and crawl spaces, where they hang inverted in their webs. They thrive in environments with high humidity and consistently low light levels. The stability of these spaces is highly valued, as the spiders prefer corners and ceilings where their irregular webs can remain intact. Garages, sheds, and rarely-used corners of attics also provide the necessary shelter for these common house spiders to flourish.
Outdoor and Natural Environments
While they are well-known for their indoor presence, cellar spiders originally evolved to inhabit natural sheltered locations. Their native environments are typically dark, humid, and stable, much like the basements they now occupy. These natural dwelling places include caves and rock crevices, which offer consistent temperature and moisture levels year-round. They are also found outdoors under loose bark on trees, beneath logs, or within abandoned animal burrows, particularly in areas that are shaded and protected from direct weather exposure.
Why They Seek Human Structures
Cellar spiders are drawn into man-made structures primarily because these places provide a stable microclimate that protects them from environmental extremes. Indoors, they avoid harsh conditions like freezing winters and excessive summer heat or drought. The interior of a home also provides a stable food supply, attracting the spiders with a consistent buffet of other household pests. Their diet includes flies, silverfish, and other spiders, and they are known to prey on species much larger than themselves, including black widow spiders. This stable climate and abundant prey, coupled with a lack of natural predators, makes human structures an advantageous habitat.