Harvestmen, often recognized by the common name “daddy longlegs,” are a familiar sight in many environments, yet they are frequently misunderstood creatures. Despite their resemblance to spiders, harvestmen are distinct arachnids belonging to the order Opiliones. They are easily identified by their small, often oval-shaped bodies and disproportionately long, slender legs. This group comprises over 6,650 discovered species worldwide, with many more likely awaiting identification.
Distinguishing Harvestmen from Spiders
One of the most common misconceptions about harvestmen is that they are spiders. While both are arachnids, harvestmen possess several key differences that set them apart from true spiders (order Araneae). A primary distinction lies in their body structure; harvestmen have their cephalothorax (head and thorax) and abdomen broadly joined, creating a single, oval-shaped body appearance, unlike spiders which have two distinct body segments connected by a narrow waist.
Harvestmen also lack the ability to produce silk, meaning they do not spin webs to catch prey. They also lack venom glands, making them non-venomous. They breathe through tracheae, a system of tubes, unlike the book lungs found in spiders. Harvestmen possess only two simple eyes, unlike spiders which generally have six or eight.
Unique Physical Traits
Harvestmen have several unique physical traits. Their body is typically small, ranging from 2 to 10 millimeters in length, and has a fused, globular, or oval shape, giving the appearance of a single body segment. From this compact body extend eight long, slender legs, which are a hallmark feature of many species. These legs are not solely for walking; the second pair is often particularly elongated and functions as sensory organs, feeling the environment ahead like antennae.
Autotomy, the ability to shed a leg when threatened, is a defense mechanism. The detached leg can continue to twitch for some time, distracting the predator while the harvestman escapes, though the lost leg does not regenerate. Their two simple eyes are positioned on a raised turret-like structure, called an ocularium, near the center of their body.
Life and Habits
Harvestmen are found globally, inhabiting a diverse range of terrestrial environments. They commonly prefer damp, dark places, such as under rocks, logs, leaf litter, and in basements or crawl spaces, as they are susceptible to dehydration. Many species are nocturnal, becoming active foragers and hunters during the night.
Their diet is varied; harvestmen are omnivorous scavengers. They consume decaying plant and animal matter, fungi, and small insects like aphids. Unlike other arachnids, they ingest solid food using pincer-like mouthparts (chelicerae), rather than external digestion. Some species exhibit gregarious behavior, gathering in large groups, which may serve as a collective defense against environmental extremes or predators. When disturbed, harvestmen may display a “bouncing” or vibrating motion, deterring potential threats.
Harmlessness to Humans
Despite their spider-like appearance, harvestmen pose no threat to humans or pets. A persistent urban legend claims they possess venom but cannot bite humans; however, this is false.
Their chelicerae, while capable of tearing food, are too small and weak to pierce human skin. Harvestmen are docile creatures that prefer to avoid confrontation. They can be beneficial inhabitants of gardens, as their omnivorous diet includes small pests and decaying organic matter, contributing to ecosystem health.