Cellar Spider, Pholcus phalangioides

The Cellar Spider (Pholcus phalangioides), known also as the Skull Spider because of its cephalothorax resembling a human skull, is a spider belonging to the family Pholcidae. The females have a body length of about 9 millimeters; the males are slightly smaller. The legs are about 5 to 6 times the length of the body. Its habit of living on the ceilings of room, garages, caves, or cellars gives rise to one of its common names. They are thought to be beneficial in some parts of the world because they kill and eat other spiders, including species that are venomous to humans such as Hobo and Redback Spiders.

As a species originally restricted to warmer portions of the west Palearctic, through the aid of humans, this synanthrope now occurs throughout a large portion of the world. It’s unable to survive in cold weather, therefore, it is restricted to houses in some parts of its range.

This is the only spider species described by the Swiss entomologist Johann Kaspar Fussli who initially recorded it for science in 1775. Confusion frequently arises over its common name because “daddy longlegs” is also applied to two other unrelated arthropods: the Harvestman and the Crane Fly.

This species has the habit of shaking its web violently when disturbed as a defense mechanism against its predators. It can easily catch and eat other spiders, mosquitoes, other insects, and woodlice. When food is inadequate, it will prey on its own kind. Rough handling will cause some of the legs to detach.

Because the originally came from the subtropics, these spiders don’t seem to be influenced by seasonal changes and breed at any time of the year. The female holds the 20 to 30 eggs in her pedipalps. The spiderlings are transparent with short legs and change their skin roughly 5 or 6 times as they mature.

An urban legend says that Pholcidae are the most venomous spiders in the world, but this claim has been proven inaccurate. Recent research has shown that pholcid venom has a rather weak effect on insects. In the Myth Busters episode “Daddy Long-Legs” it was shown that the spider’s fangs, which are .25 millimeters long, could penetrate human skin about .1 millimeters but that only a very mild burning sensation was felt for a few seconds.

Image Caption: Pholcus phalangioides. Credit: Olaf Leillinger/Wikipedia (CC BY-SA 2.5)