The Phalangids or Opiliones (better known as "harvestmen" or "daddy longlegs") are eight-legged invertebrate animals belonging to the order Opiliones in the class Arachnida, in the subphylum Chelicerata of the phylum Arthropoda. As of 2000, over 5,000 species of Phalangids have been described worldwide.

The name "daddy longlegs" can also refer to two other unrelated arthropods: the crane fly (Tipulidae) and the cellar spider (Pholcidae).

Physical description

These harmless arachnids are known for their exceptionally long walking legs, compared to body size. The difference between harvestmen and spiders is that in harvestmen the two main body sections (the prosoma and opisthosoma ) are nearly joined, so that they appear to be one structure. They have two eyes, oriented sideways. They have scent glands that secrete a peculiar smelling fluid when disturbed. Harvestmen do not have silk glands and most do not possess poison glands. Those that do have venom pose absolutely no danger to humans (see below).

Most species live for a year or two.

Behavior

Many species are omnivorous, eating primarily small insects; some are scavengers. Mating involves direct copulation, rather than the deposition of a spermatophore.

A poisonous myth

There is an urban legend claiming that the daddy longlegs is the most poisonous spider in the world, only its fangs are too small to bite a human, and is thus not actually dangerous. This is untrue on several counts. First, of course, phalangids are not spiders. Many species don't have any poison glands at all. Of those that do, the venom appears to be far less toxic than that of a black widow spider. The size of the fangs varies by species, of course, but even those with relatively long fangs do not bite humans (or other large creatures). The urban legend is probably due to confusion with the Daddy long-legs spider, which can indeed bite and is indeed poisonous, but not dangerously so. More can be read on the debunking of this myth on the Daddy long-legs spider page.