The creature commonly known as a “Daddy Long-Legs” often causes confusion because its spindly appearance resembles a spider. Despite this, harvestmen are not true spiders, though they belong to the same extended family of arachnids. The misidentification stems from their eight legs and small, globular bodies. Harvestmen represent a distinct and ancient lineage that separated from true spiders millions of years ago.
The Definitive Answer: Taxonomy and Classification
Harvestmen and true spiders both belong to the Class Arachnida, which encompasses all eight-legged arthropods, including mites, ticks, and scorpions. Their classification diverges at the Order level. True spiders are categorized in the Order Araneae, defined by characteristics such as the ability to produce silk.
Harvestmen belong to their own separate Order, Opiliones. The two groups share a common ancestor but have evolved independently for a long period, resulting in fundamental differences in structure and behavior.
Distinguishing Features: Harvestmen vs. True Spiders
The primary physical difference between a harvestman and a true spider is the structure of its body. Spiders have two distinct sections—the cephalothorax and the abdomen—connected by a narrow pedicel, creating a characteristic “waist.” Harvestmen, in contrast, have these two sections broadly joined, making their body appear as a single, fused, oval-shaped unit.
Harvestmen lack two defining features of true spiders: silk glands and venom glands. Since they cannot produce silk, harvestmen do not build webs, relying instead on active hunting or scavenging. The common myth that harvestmen possess potent venom is untrue, as they are completely non-venomous.
Harvestmen also have a different arrangement of eyes compared to most spiders. While true spiders typically possess six or eight eyes, a harvestman generally has only two simple eyes. These eyes are usually mounted on a raised structure in the middle of the cephalothorax called an ocularium.
Unique Lifestyle and Habits of Harvestmen
The absence of venom and webs reflects the harvestman’s unique ecological role as primarily scavengers and omnivores rather than dedicated predators. Their diet is highly varied, consisting of decaying plant matter, fungi, bird droppings, dead organisms, and small, soft-bodied insects. Unlike spiders, which consume their prey by liquefying it and sucking the contents, harvestmen can tear off and ingest small chunks of solid food.
Harvestmen employ specific behaviors for defense and navigation. When threatened, they can use autotomy, intentionally detaching a leg to distract a predator. The severed leg will continue to twitch vigorously for a period, allowing the harvestman to escape unharmed. They also possess defensive glands that release a foul-smelling secretion when disturbed.
Since their two eyes are generally poor at forming clear images, harvestmen rely heavily on touch and chemical cues to navigate their environment. They frequently use their second pair of legs, which are often the longest, as sensory feelers. These legs are constantly tapped on the ground ahead of them, functioning much like antennae to explore their surroundings and locate food.