Cellar spiders, belonging to the family Pholcidae, are common arachnids found throughout the world. Despite their widespread presence, cellar spiders are generally harmless to people, playing a beneficial role in their environment.
Identifying a Cellar Spider
Cellar spiders are easily recognizable. They possess extremely long, thin, and delicate legs that are disproportionately long compared to their small body size, typically no more than about a quarter-inch (6 mm) in length. Their coloration usually ranges from gray to tan or yellowish. Many common species have eight eyes arranged in three groups, with two in the center and a cluster of three on each side of the central pair.
These spiders are often colloquially referred to as “daddy longlegs” due to their spindly appearance. However, they are distinct from harvestmen (Opiliones), also called “daddy longlegs,” which are not true spiders. Cellar spiders have two distinct body segments (a cephalothorax and abdomen) and produce silk, whereas harvestmen have a single, fused, oval-shaped body and do not spin webs or possess venom glands. If a long-legged arachnid is found in a web, it is likely a cellar spider.
Habitat, Diet, and Behavior
Cellar spiders prefer dark, damp, and undisturbed environments. They are frequently encountered in basements, cellars, attics, garages, and quiet corners of rooms. They can also be found in natural settings like caves and rock piles. These spiders construct irregular, non-sticky webs, often in corners or crevices, where they typically hang upside down.
Their diet primarily consists of small insects and other arthropods that become ensnared in their webs, including flies, mosquitoes, gnats, and moths. Cellar spiders are also known to prey on other spiders, sometimes even larger species like black widows, by casting long swaths of silk to bind them from a safe distance. They employ a unique hunting technique: vibrating their web to ensnare prey or mimicking a struggling insect in another spider’s web to lure the host out. When disturbed, cellar spiders rapidly vibrate or bounce in their webs, creating a blur that makes them difficult for potential predators to pinpoint.
Dispelling Common Myths
A widespread misconception suggests cellar spider venom is extremely potent but their fangs are too short to bite humans. This is a myth; while cellar spiders do produce venom, like most spiders, it is considered mild and not dangerous to humans. Their fangs are small, but they are capable of penetrating human skin, though bites are rare and result in minimal, non-severe reactions like mild redness or irritation, if any. There are no documented medical cases of cellar spider bites causing harm to humans.
Cellar spiders are, in fact, considered beneficial housemates. They act as natural pest control agents by preying on various household insects and other spiders, helping to manage pest populations. Their presence can indicate a healthy indoor ecosystem and they do not cause structural damage to homes. These spiders are non-aggressive and will retreat or vibrate their webs when approached, posing no threat to humans or pets.