Like all spiders, cellar spiders have two body-segments, a cephalothorax in front and an abdomen behind. They have eight legs, all attached to the cephalothorax. Cellar spiders have very long thin legs compared to other spiders. Their legs are many times longer than their bodies. Because of this they are sometimes called "daddy longlegs spiders", though they are not related to the other "daddy longlegs," which are Harvestmen. On the front they have two small "mini-legs" called palps. These are used to grab prey, and in mating, and are much bigger in male spiders than in females.
Different species of cellar spiders have six or eight eyes, and the size and arrangement of eyes is different in different groups. Cellar spiders have fangs that they use to bite their prey with, and have venom glands, but their fangs are very short. Their color varies from light tan to grayish-brown.
Female cellar spiders are often much bigger than males.
There are hundreds of species of cellar spiders found all over the world. One species in particular, Pholcus phalangioides, is particularly comfortable living in houses and other buildings, and so has been spread all around the world by people moving around. Only a few species occur in Michigan, but they are common in basements and unused buildings.
These spiders prefer to live in dark places: in caves, cracks and crevices in rocks, unused animal burrows, and in the dark and quiet parts of buildings.
Cellar spiders hatch from eggs, and the hatchlings look more or less like grown-up spiders, though sometimes their colors change as they age. To grow they have to shed their exoskeleton, which they do many times during their lives.
We don't know for sure how long these spiders live, probably only a few years at most, and very few probably make it that long.
Most cellar spiders don't move around too much, they usually stay with their web, or raid nearby webs. They often hang upside down while waiting for prey to touch their webs. They are not social animals, they only come together to mate.
Spiders in this group probably use touch and chemicals to communicate, though they can see too. They are also very sensitive to vibrations in their webs.
Like all spiders, cellar spiders are predators. They eat insects, spiders, and other small invertebrates. They spin a large loose, three-dimensional web (not flat like orbweavers) that is not sticky. They use their web as a kind of prey-detection system. When a passing insect bumps into it, they come running out and grab it and bite it, then wrap it in silk. Ants are particularly common prey.
Many cellar spiders also raid the webs of other spiders, eating their prey and the spiders themselves. They sometimes hunt around the edges of the webs of female spiders of other species. Males who come to mate with the female may get eaten by the cellar spider instead.
Cellar spiders mainly avoid predators by living in dark places. If their web is touched, they sometimes vibrate back and forth very fast. We don't know for sure why they do this, maybe to make themselves harder to see.
These spiders are not dangerous to people, and they sometimes eat insects that are pests to humans.
No cellar spider species are known to be endangered.