Invertebrates
Harvestman
Opiliones · also called daddy longlegs, harvest spider, shepherd spider
Almost everyone has heard that daddy longlegs are the most venomous creatures alive but simply cannot bite through human skin. It is a great story. It is also completely false, and the animal it is usually told about, the harvestman, is not even a spider.
Overview
The harvestmen are an arachnid order, Opiliones, with about 6,600 species worldwide. They are found on every continent except Antarctica, in leaf litter, on tree trunks and walls, in caves, and around buildings. A harvestman is an omnivore and scavenger that, unlike a spider, can chew and swallow solid food.
How to know it is not a spider
A spider has two body sections joined by a waist; a harvestman’s body is a single oval with no waist. It has no silk, so it builds no web, and it has no venom and no fangs — so the famous myth has nothing to measure.
Legs that escape
Most harvestmen have just two eyes on a small central turret and navigate mainly with their long second pair of legs, used like feelers. A seized leg detaches and keeps twitching to distract a predator, and never grows back.
Status
Not Evaluated as a group. Most species are common; a minority of cave and range-restricted species are of concern.
Harvestman: common questions
Is it true that daddy longlegs are the most venomous animals but their fangs are too small to bite?
No. This is one of the most widely repeated animal myths, and it is wrong on every count. Harvestmen have no venom glands at all and no fangs, so there is nothing to measure. The myth may partly come from confusion with the cellar spider, a long-legged spider also called daddy longlegs, which does have venom, but its venom is not medically significant to humans either, and tests have shown its bite produces at most a brief mild sting. Neither animal is dangerous. A harvestman cannot bite a person in any meaningful way, because its mouthparts are tiny chewing structures, not piercing fangs.
What is the difference between a harvestman and a cellar spider?
They are often both called daddy longlegs but they are only distantly related. A harvestman has a single compact oval body, two eyes on a central bump, no silk, and it walks about in the open on leaf litter, walls, and tree trunks. A cellar spider is a true spider with two body sections joined by a narrow waist, eight eyes, and silk glands, and it hangs upside down in a loose, messy web in the corner of a room or cellar, where it spins prey in silk. If it is in a web, it is a spider; if it is roaming free with a one-piece body, it is a harvestman.
Why do harvestmen gather in large clumps?
In some parts of the world, particularly with certain species, hundreds or even thousands of harvestmen pile together in a dense, pulsating mass on a cave wall, cliff overhang, or tree trunk, especially in the dry season or before winter. The aggregation is thought to reduce water loss by lowering the surface area exposed to the air, to buffer temperature, and to multiply the effect of the defensive stink glands, so a predator that disturbs the clump gets a much bigger dose of repellent chemicals and the sight of a shivering wall of legs. The individuals are not truly social; they simply benefit from crowding.
Do harvestmen bite or hurt people, plants, or crops?
No to all three. Harvestmen have no venom, cannot pierce human skin, do not feed on living plants in any damaging way, and are not agricultural or household pests. They are quiet, harmless animals that spend their time cleaning up dead insects, fungi, and decaying matter in gardens, woods, and outbuildings, which makes them mildly beneficial. The only nuisance is aesthetic, when they gather on the outside of a house or in a shed, and even then they do no harm and disperse on their own.