You see them almost every day, but very little is known about daddy-longlegs, also called harvestmen. They are not spiders, but belong to a group with many different species, called Opiliones. The common name, daddy-longlegs, likely came about because of their small oval body and long legs, and the name harvestman because they are most often seen in large numbers in the fall around harvest time.
While they have eight legs and an outward appearance of a spider, daddy-longlegs lack two of the most important features that make a spider a spider: silk production and venom. Daddy-longlegs do not have spinnerets that spiders have to produce silk and make webs. Spiders also produce venom they inject through fangs to quickly kill and digest prey. Daddy-longlegs do not produce venom, nor do they have fangs. A very popular urban legend states that the daddy-longlegs are the most poisonous spiders in the world, but their fangs are too small to penetrate human skin. This is false. Daddy-longlegs have mouthparts similar to those of crabs or scorpions that they use to hold prey while they eat. To protect themselves, daddy-longlegs produce a pungent odor most predators find distasteful.
The body of most adult daddy-longlegs is about 1/16-1/2 inch long, oval with very long legs. Males tend to have smaller bodies than females but they have longer legs. Legs easily break off. The ability to break off legs is similar to the ability of lizards to break off a portion of their tail if being attacked by a predator. The second pair of legs are the longest and are used as a sensory structure similar to the way insects use their antennae.
Female daddy-longlegs lay their eggs in soil, under stones, or cracks in wood. The eggs are laid in the autumn and hatch in the spring. In the northern areas of the United States, daddy-longlegs live for only one year. In South Carolina and the rest of the southeast, daddy-longlegs can overwinter as adults and live for up to two years.
Daddy-longlegs are generally beneficial. They have a very broad diet that includes spiders and insects, including plant pests such as aphids. Daddy-longlegs also scavenge for dead insects and will eat bird droppings. In the fall, they can become a nuisance when they congregate in large clusters on trees and homes, usually around eves and windows. Additionally they can be found in damp crawl spaces, unfinished basements, and garages. Rarely are daddy-longlegs encountered inside finished, living spaces of homes.
Since daddy-longlegs are beneficial predators and scavengers in nature, control should only be performed when absolutely necessary. The clustering behavior only occurs during the fall and for only a brief period of time. Daddy-longlegs do not damage structures when they cluster. If control is necessary, due to a large number of daddy-longlegs that is considered unpleasant, insecticide sprays labeled for exterior use on spiders can also be applied directly to daddy-longlegs found outdoors. However, in nearly all situations, chemical control is not necessary. Most daddy-longlegs can be removed from structures with a vacuum or broom.