The long-bodied cellar spider (Pholcus phalangioides) is a globally distributed arachnid frequently found in human dwellings. Despite its alarming appearance due to its extremely long legs, this spider poses no danger to people or pets. They are common in the dark, quiet corners of basements, cellars, and garages. The species is non-aggressive and entirely harmless.
Correct Identification and the “Daddy Long Legs” Confusion
The long-bodied cellar spider is often misidentified because it shares the common name “Daddy Long Legs” with two other, unrelated groups of arthropods. Confusion often arises with Harvestmen (Opiliones), which are arachnids but are not true spiders as they lack silk glands and venom. The cellar spider is a true spider belonging to the family Pholcidae.
This spider has a small, pale, cylindrical body, measuring 6 to 8 millimeters in length. Its most notable feature is its eight extremely thin legs, which can be five to six times the length of its body, sometimes reaching 50 millimeters. They construct large, messy, irregular webs in sheltered areas. When disturbed, they vibrate rapidly in their web, a defensive behavior intended to blur their outline.
Analyzing Venom and Bite Risk
An urban legend claims that cellar spiders possess potent venom but have fangs too small to bite humans. This assertion is false; their venom is not medically significant to people. Scientific examination shows the venom is relatively weak, even against insect prey.
The belief that their fangs are too small is also a misconception. Their chelicerae, or fangs, measure about 0.25 millimeters, which is long enough to penetrate the human epidermis (less than 0.1 millimeters thick). While they can bite, reports are extremely rare because they are timid and non-aggressive. A bite, should it happen, causes only a mild, short-lived stinging sensation with no lasting effects.
Ecological Role and Household Benefits
The long-bodied cellar spider frequently lives indoors, providing a natural form of pest control. The species is carnivorous, preying on nuisance insects that enter the home, including mosquitoes, flies, and other small arthropods.
The cellar spider is also an aggressive predator of other, often larger, spiders. They actively invade the webs of species like the hobo spider and the venomous Redback spider. They use their long legs to ensnare the occupant with silk before delivering a disabling bite. By targeting other arachnids, Pholcus phalangioides helps limit the population of other spiders sharing the indoor environment.