Harvestman (order Opiliones)

Although I freak out around spiders (one time I ran to the other side of a forest because a spider startled me in a tree), people are always surprised at my nonchalant attitude towards daddy longlegs. They just don’t look that much like spiders to me — with their extremely spindly legs and tiny bodies, they really have no substance to them at all.

One of the reasons I may not be afraid of daddy longlegs (or harvestmen, as they are more properly known) is that they are not spiders at all — they are classified in the order Opiliones, and are more closely related to scorpions than spiders. There are over 6,500 species of harvestmen, and they are found on every continent except Antarctica.

Such nice long legs they have! Image source: Wikipedia

Such nice long legs they have!
Image source: Wikipedia

There are a couple of things that make harvestmen quite different from your run-of-the-mill spider. Though they do have the typical head and abdomen of spiders, the place where the two segments meet is very wide, which makes it appear as if harvestmen only have one body segment. Not all harvestmen have super long legs, but most species are known for this trait. Harvestmen do not have silk glands, and thus cannot produce webs. They also lack the spiders’ four pairs of eyes, and usually have only a single pair, though some species are eyeless. Harvestmen don’t have antennae, so they use their second pair of legs to feel their way around. The largest body size for a harvestman is 2.2 cm, and the longest leg span is 34 cm, which actually does seem a little terrifying.

Another difference between harvestmen and spiders is the harvestman’s ability to consume solid food. They are generally omnivorous, eating insects, plant matter, fungi, and other delicious things. Some harvestmen hunt, though many are scavengers. After eating, harvestmen do the polite thing and clean their legs, wiping each one with their mouths.

A true spider often also called 'daddy longlegs'. This is actually a cellar spider, and they are not harvestmen. Image source: http://spiderhugger.com/category/species/pholcus/

A true spider often also called ‘daddy longlegs’. This is actually a cellar spider, and they are not harvestmen.
Image source: http://spiderhugger.com/category/species/pholcus/

When I was a kid I was told that harvestmen are the most venomous animal in the world, but lack the necessary fangs and strength to pierce human skin, and are thus harmless. This is only partly true; their mouths are fairly weak. The part about the venom is nonsense — harvestmen do not possess any venom glands.

Mating in harvestmen occur internally, with the male sometimes offering the female some tasty saliva from his mouth before copulation. Some species of harvestmen build nests for their eggs, while in others the male is responsible for guarding and cleaning the eggs. This male guarding is unique to harvestmen amongst the arachnids.

A great big group of harvestmen. This picture gives me the creeps. Image credit: Luis Fernández García via Wikipedia

A great big group of harvestmen. This picture gives me the creeps.
Image credit: Luis Fernández García via Wikipedia

Being small and spindly creatures, harvestmen are the targets of quite a lot of predation. To try and deal with this, harvestmen have developed a number of potentially life-saving strategies. One tactic involves gluing debris on their bodies, while in another harvestmen play dead. Other species bob up and down to confuse predators, and all harvestmen have scent glands that can emit nasty smelling substances. Some species will congregate in large numbers, partly due to climactic reasons, but also to deter predators. Some groups of harvestmen can reach over 70,000 individuals. When a harvestman is attacked and a leg is detached, the leg will keep twitching, serving as a decoy for predators.

Unfortunately writing this has made me more afraid of harvestmen — I especially don’t like the sound of 70,000 harvestmen all in one place. Still, these guys are nothing compared to real spiders, so I’m happy to leave them alone if I find them in my house.

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3 thoughts on “Harvestman (order Opiliones)

  1. Pingback: Quokka (Setonix brachyurus) | Our Wild World

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