Harvestmen, often seen in gardens and homes, are long-legged arthropods belonging to the genus Leiobunum. Their distinct, long, thin legs often lead people to question whether these creatures pose any danger. Concerns about their potential toxicity are common but are largely based on persistent misinformation.
What Exactly Are Harvestmen?
Harvestmen belong to the class Arachnida, relatives of spiders and scorpions, but they are classified in their own distinct order, Opiliones. They differ from true spiders (order Araneae) because their cephalothorax and abdomen are broadly joined and fused. This results in only one apparent body section, lacking the narrow waist seen in spiders.
Most species of harvestmen, including Leiobunum, possess only two eyes, typically mounted on a small, raised tubercle. Their eight legs are disproportionately long. The second pair functions primarily as sensory organs, allowing them to probe their environment. This sensory function is crucial since their eyes only sense light and dark, unable to form detailed images.
Dispelling the Poisonous Myth
The definitive answer regarding the safety of Leiobunum is that they are neither venomous nor poisonous. Venom is a toxin actively injected into another organism, usually through a bite or sting. Poison causes harm when ingested, inhaled, or absorbed through the skin.
Harvestmen lack the specialized anatomy required to produce or deliver venom, including the venom glands used by true spiders. Their mouthparts, known as chelicerae, are small, claw-like structures used for grasping and chewing food, not hollow fangs designed for injection. Since they have no mechanism for injection or harmful toxins, they are neither venomous nor poisonous.
Why the Confusion Exists
The belief that harvestmen are dangerous stems from confusion surrounding the common name “Daddy Longlegs.” This term is used interchangeably for three unrelated arthropods: the harmless harvestman (Leiobunum), Cellar Spiders (true spiders), and Crane Flies (insects).
The most persistent urban legend claims the “Daddy Longlegs” possesses potent venom but has fangs too short to bite humans. This myth is incorrectly applied to the harvestman. While the Cellar Spider (a true spider) does have weak venom, it is not medically significant to humans. The baseless myth is mistakenly assigned to the harmless harvestman, which has no venom.
Harmless Defense Mechanisms and Diet
When threatened, Leiobunum employ defense mechanisms focused solely on repelling or distracting a predator, not on causing harm. Harvestmen possess a pair of prosomatic scent glands, called ozopores, located on their body. When disturbed, they release a foul-smelling secretion from these glands, a noxious chemical defense intended to make them unappealing to an attacker.
Another common defense is leg autotomy, where the harvestman voluntarily detaches a leg when grasped. The detached leg continues to twitch, distracting the attacker and allowing the harvestman to escape. Harvestmen are beneficial omnivores and scavengers. Their diverse diet consists of small, soft-bodied invertebrates, dead organisms, fungi, and plant matter.