The common "Harvestman" name is because they are frequently encountered under trees during the harvest season.(1)
Numbers
>6600 species worldwide arranged into ~45 families of 4 suborders (of which Laniatores is by far the largest, with >4100 species)(2)(3)(4)
Size
body from millimeters to centimeters
Identification
Easily separated from spiders by the broad fusion of the two body segments, so that the body appears to be composed of a singular segment. Harvestmen do not possess silk glands, and can't spin webs. Unlike spiders, harvestmen lack venom glands associated with their chelicerae (mouthparts). Uniquely among the arachnids fertilization is direct: males of most taxa possess a penis (also referred to in the literature as pene, aedagus or intromittent organ).
Almost all long-legged harvestmen observed "wandering" or exposed in habitats, either during daylight hours or at night, will represent members of the suborder Eupnoi. The most conspicuous/photographed taxa in North America include members of the Phalangiidae & Sclerosomatidae (Leiobunum in particular).
forests, grasslands, wetlands, mountains, caves, chaparral, and anthropogenic habitats
Season
"Daddy-long-legs" are not likely to be found in winter months in northern/montane regions, except as overwintering populations in refugia (e.g., caves). However, many of the small-bodied reclusive taxa are only winter active.
Food
Carnivorous, feeding on a variety of small arthropods
Life Cycle
Egg, juvenile, adult. Most reproduce sexually (direct fertilization, males possess a penis); a handful parthenogenetically (i.e., without males).
Remarks
Although often mistaken for spiders, these arachnids are more closely related to scorpions(3)
In some cases, in dry climates, they gather in large numbers during the day, probably to avoid dessication, and wander about in search of food after the sun goes down.
Photo taken in Sierra Madre, Mexico
Opiliones have a chemical defense from glands at the base of the front legs.(1)
The exceptionally long second pair of legs are used in place of antennae.(5)
Is the "Daddy Long-Legs" the most venomous spider? NO...Absolutely Not
Two groups of arachnids are commonly called "Daddy Long-legs" but neither are dangerous to people.
Group I: Opiliones (=Phalangida), "Harvestmen" --Commonly called "Daddy Long-legs," they DO NOT POSSESS VENOM nor a delivery system (see here)
Group II: Araneae (True Spiders), family Pholcidae, "Cellar Spiders" --true spiders with mild venom that is not considered dangerous to vertebrates, incl. humans (see here)
Wood, H. C. 1868. On the Phalangeae of the United States of America. Communications of the Essex Institute 6: 10-40.
Weed, C. M. 1893. A descriptive catalogue of the harvest-spiders (Phalangiidae) of Ohio. Proceedings of the United States National Museum 16 (950): 543–563.
Banks, N. 1901. Synopses of North-American Invertebrates. XVI. The Phalangida. American Naturalist 35: 669-679.
Bishop S.C. (1949) The Phalangida (Opiliones) of New York. Proc. Rochester Acad. Sci. 9: 159-235.Full text
Hedin M., Starrett J., Akhter S., Schönhofer A.L., Shultz J.W. (2012) Phylogenomic resolution of Paleozoic divergences in harvestmen (Arachnida, Opiliones) via analysis of next-generation transcriptome data. PLoS ONE 7(8): e42888 (Full text)
