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Order Opiliones - Harvestmen

Harvestman Harvestman Harvestmen Opiliones Orange Harvestman - Leiobunum politum Harvestman - Leptobunus californicus Opiliones mating dance? - Leiobunum vittatum - male - female spider
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Chelicerata (Chelicerates)
Class Arachnida (Arachnids)
Order Opiliones (Harvestmen)
Other Common Names
English: Daddy-long-legs/Daddy-longlegs/Daddy Long-legs, Granddaddy-long-legs, Harvest Spiders, Shepherd Spiders, Phalangids, Opilionids; French: faucheux, opilions; German: Weberknechte.
Synonyms and other taxonomic changes
Nomenclature has changed over the years with the group. One order name common in older literature is Phalangida. The suborder nomenclature has also changed several times and may not yet be stable. The 4 suborders referred to in the Count section below break suborder Palpatores into suborders Dyspnoi and Eupnoi.
>6500 species worldwide arranged into 46 families of 4 suborders (of which Laniatores is by far the largest, with >4100 species)(1)(2)(3)
Variable; body sizes range from a few millimeters to a few centimeters. Legs are several times the size of the body in the more familiar "daddy-long-legs" forms of the Phalangioidea.
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. Also, as they do not possess silk glands, harvestmen can't form webs. Uniquely among the arachnids fertilization is direct: males possess a penis (also referred to in the literature as pene, aedagus or intromittent organ).
Global, except Antarctica(2)
All habitats (except possibly deserts) in Canada & the US: forests, grasslands, wetlands, mountains, caves, chaparral, and anthropogenic habitats.
Not likely to be found in winter months in northern/montane regions, except as overwintering populations in refugia (e.g., caves).
Life Cycle
Egg, juvenile, adult. Some reproduce sexually (direct fertilization, males possess a penis); others, parthenogenetically (i.e., without males).
Although often mistaken for spiders, these arachnids are more closely related to scorpions(2)
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, sierra Madre. file00202001.w

MYTH BUSTER ... "Stop the Urban Legend!"
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)
Print References
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)
Works Cited
1.Order Opiliones Sundevall, 1833. In: Zhang Z.-Q. (ed.) Animal biodiversity: An outline of higher-level classification...
Kury A.B. 2013. Zootaxa 3703: 27–33.
2.Kury A.B. (-2014) Classification of Opiliones
3.Kury A.B., ed. (2009) Project Opilionomicon. Museu Nacional, UFRJ, Rio de Janeiro
4.Spiders and Their Kin: A Golden Guide from St. Martin's Press
Herbert W. Levi, Lorna R. Levi, Nicholas Strekalovsky. 2001. St. Martin's Press.
5.Harvestmen: The Biology of Opiliones
Ricardo Pinto-Da-Rocha, Glauco Machado, and Gonzalo Giribet (eds.). 2007. Harvard University Press.