Cellar spiders are very common and make up the most common members of the Pholcidae family of spiders in the United States. They have extremely long legs so are sometimes called daddylong-legs spiders, but are not daddylong-legs. They are true spiders and are found in many types of structures (homes, garages, sheds, cellars, offices, etc.) at any time of the year. They like places that are dark, dry, quiet and protected. They can develop large populations but are not harmful or dangerous to humans, as their mouthparts are too small and weak to be able to bite a person. They can become a pest or a nuisance due to the large amount of webbing they produce in order to catch their prey. They can be seen hanging upside down on their webs, waiting for their victims to become entangled.
Additional Information: Longbodied Cellar Spider (Penn State)