Harvestmen are a widespread group of arachnids often encountered in gardens, forests, and damp, dark places around the world. These creatures belong to the scientific order Opiliones, which includes over 6,650 discovered species. Though frequently mistaken for spiders, harvestmen are a separate and distinct lineage within the class Arachnida.
Distinct Physical Anatomy
The most distinctive anatomical feature of a harvestman is its body structure, which appears to be a single, oval segment. Unlike true spiders (Order Araneae), which have two clearly separated body regions—the cephalothorax and the abdomen—harvestmen have these two sections broadly fused together. This fusion creates a compact, globular body.
Harvestmen typically possess only one pair of eyes, totaling two, positioned on a raised turret-like structure on the top of the cephalothorax. In contrast, most spiders have four pairs of eyes, totaling eight. They lack the fangs and venom glands characteristic of spiders, rendering them harmless to humans. Their chelicerae, or mouthparts, are modified into small, pincer-like structures used for tearing and chewing solid food.
Harvestmen are recognized for their eight extremely long, thin legs, which can span many times the length of their bodies. The first and third pairs of legs are primarily used for walking and support. The second pair of legs is noticeably the longest and functions as specialized sensory appendages, constantly tapping and exploring the environment like antennae. This second pair is rich in sensory receptors that help the harvestman navigate, locate food, and detect threats. Harvestmen also lack the silk-producing spinnerets found on spiders and are incapable of producing webs.
Ecology, Diet, and Behavior
Harvestmen are found on nearly every continent, thriving in diverse habitats ranging from tropical forests to temperate grasslands and caves. They prefer moist, dark environments, which helps prevent dehydration. This often leads to them being discovered under rocks, leaf litter, or in the damp corners of basements and sheds.
The diet of an Opilione is different from that of most predatory arachnids, as harvestmen are omnivorous scavengers. They use their chewing mouthparts to consume a wide variety of materials, including small, soft-bodied insects, mites, and insect eggs. They commonly feed on decaying organic matter, such as dead insects, fungi, and plant material like rotting fruit.
To defend against predators, harvestmen employ several survival strategies. They possess a pair of prosomatic defensive scent glands, called ozopores, that release a pungent, foul-smelling chemical fluid when disturbed. This chemical defense is distasteful and deters small mammals and birds. A more dramatic mechanism is autotomy, the ability to voluntarily detach one or more legs when seized by a predator. The detached leg continues to twitch, which distracts the attacker and allows the harvestman to escape.
Clarifying Common Misidentifications
The common name “daddy long-legs” is a source of frequent confusion because it is applied to three distinct types of organisms. This name refers to the harvestman (Order Opiliones), the cellar spider (Family Pholcidae), or the crane fly (Order Diptera), which is an insect. Understanding the differences between these groups is necessary to avoid misidentification.
Harvestmen are easily distinguished from true spiders (Order Araneae) by their body plan and lack of certain features. Spiders have a constriction between their two body segments, possess fangs, and produce silk. Harvestmen have a fused body, no fangs, and no silk. Crane flies, the third “daddy long-legs,” are insects with six legs and wings, and their adult forms are non-venomous and incapable of biting.
The most persistent myth surrounding harvestmen is the claim that they possess potent, deadly venom but cannot bite humans because their fangs are too short. This is completely false, as harvestmen do not have venom glands or fangs. This myth likely stems from confusion with the cellar spider, which is a true spider and produces venom, although its venom is not dangerous to humans. Harvestmen are entirely non-venomous and pose no threat to people.