The common name “granddaddy long leg” is one of the most ambiguous terms in the world of arthropods, frequently leading to confusion about which creature is being discussed. This single, familiar name is applied to at least two entirely different types of arachnids and sometimes even to a type of insect. To clarify this widespread misunderstanding, we must examine the physical characteristics and behaviors of the two primary candidates for this common moniker.
The True Harvestman (Opiliones)
The creature most frequently referred to as a granddaddy long leg in North America is the Harvestman, belonging to the Order Opiliones. These animals are arachnids, related to spiders, but they are distinctly not spiders themselves. The most telling feature is their body structure, which appears as a single, fused oval segment, lacking the narrow waist seen in true spiders.
Harvestmen possess eight legs, often appearing disproportionately long and thin relative to their tiny, pill-shaped body, which typically measures less than a quarter-inch. They use their second pair of legs not for walking, but as sensory feelers to explore their environment and detect prey. When threatened, they can voluntarily detach a leg, a defense mechanism called autotomy; the severed limb continues to twitch, distracting a potential predator. Another defense is the release of a foul-smelling chemical secretion from specialized scent glands, making the Harvestman unappetizing to attackers.
The Cellar Spider Confusion (Pholcidae)
Another group frequently called “granddaddy long legs” is the Cellar Spider, which belongs to the Family Pholcidae, and these are true spiders. Unlike the Harvestman, the Cellar Spider’s body is clearly divided into two distinct segments: a cephalothorax and a cylindrical abdomen. They possess eight extremely long and fragile legs, giving them a wispy, delicate appearance as they hang in their irregular, messy webs.
Cellar Spiders are recognizable by their behavior, as they often hang upside down in the corners of rooms or ceilings. When disturbed, they sometimes vibrate their bodies rapidly. This vibrating motion is a defensive tactic that blurs their outline, making them difficult to target. As true spiders, Pholcidae possess silk glands and fangs, which they use to capture and subdue prey within their tangled webs.
Debunking the Venom Myth
A long-standing urban legend suggests that the granddaddy long leg is the most venomous creature in the world but cannot bite humans because its fangs are too small. This myth is demonstrably false for both candidates. Harvestmen (Opiliones) are entirely harmless to humans because they do not produce venom at all. They lack the venom glands found in spiders and rely on pincer-like jaws for grasping food, posing no danger to people.
Cellar Spiders are technically venomous, like nearly all spiders, but their venom is extremely weak and poses no medical threat to humans. Scientific analysis suggests their venom is significantly less potent than that of dangerous species, such as the brown recluse spider. Furthermore, the fangs of the Cellar Spider are typically too short and their jaw muscles too weak to effectively penetrate human skin. There is no documented case of a medically significant bite from a Cellar Spider.
Ecological Role and Habitat
Harvestmen are predominantly omnivorous scavengers, consuming a diverse diet that includes decaying plant matter, fungi, and small, soft-bodied insects like aphids. They are highly susceptible to dehydration, which is why they are often found outdoors in cool, damp, dark locations, such as under rocks, in leaf litter, or beneath logs.
Cellar Spiders are predators that use their webs to capture various small insects and other arthropods. They are particularly known for preying on other spiders, including robust house spiders and sometimes even black widows. These spiders thrive in dark, sheltered, high-humidity environments, which is why they are commonly found in basements, cellars, garages, and crawl spaces, acting as natural pest control agents.