Granddaddy long legs are not poisonous, and most of the creatures that go by that name are not even spiders. The phrase “granddaddy long legs” (or “daddy long legs”) gets casually applied to at least three completely different animals, which is the root of one of the most persistent myths in popular zoology: that they carry the world’s deadliest venom but simply cannot deliver it. The reality is far less dramatic, and the full story depends on which leggy creature you are actually looking at.
Three Animals, One Nickname
The confusion starts with the name itself. Depending on where you live and who you ask, “granddaddy long legs” can refer to harvestmen (order Opiliones), cellar spiders (family Pholcidae), or crane flies (order Diptera, which are insects with wings). These animals are not closely related to each other. Harvestmen are arachnids but belong to their own order, completely separate from spiders. Cellar spiders are genuine spiders that build messy webs in basements and garages. Crane flies are flying insects that look like oversized mosquitoes and have nothing to do with arachnids at all. When someone repeats the “most venomous but can’t bite” claim, they are usually conflating at least two of these animals into one imaginary creature.
This matters because the answer to “are they poisonous?” changes entirely based on which animal you mean. Crane flies have no venom and no interest in biting anything. Harvestmen have no venom glands whatsoever. And cellar spiders do produce venom, but research shows its effects on humans are negligible. None of the three poses any real danger to people.
Harvestmen Have No Venom at All
Harvestmen are probably the animal most people picture when they hear “granddaddy long legs,” especially outdoors. They have a small, round body with extremely long, thin legs, and they move with that distinctive bouncing gait across garden walls and forest floors. But harvestmen are not spiders. They lack the two distinct body segments that define spiders; instead, their head and abdomen are fused into a single oval structure. They do not produce silk. And critically, they have no venom glands and no fangs capable of injecting venom. They simply cannot envenomate anything.
Harvestmen eat by grasping food with small pincerlike mouthparts called chelicerae. Their diet is omnivorous. A study of seven harvestman species found that rather than being strict predators, they are what researchers call zoophytophagous, meaning they eat both animal and plant material. Their self-selected diets included significant amounts of carbohydrate, and field evidence suggested they were often carbohydrate-limited, actively seeking out plant-based food sources.
1PubMed. Macronutrient niches and field limitation in a woodland assemblage of harvestmenSo the claim that harvestmen are “the most venomous spider” fails on two counts: they are not spiders, and they have no venom. The myth likely arose because people assumed anything with eight legs and a creepy appearance must be a spider, and because the harvestman’s spindly, fragile build somehow got interpreted as evidence that it was “too delicate to bite” rather than what it actually is, which is an animal that was never built for envenomation in the first place.
Cellar Spiders Can Bite, and Their Venom Is Harmless to You
Cellar spiders are the other main animal called “daddy long legs,” and unlike harvestmen, these are true spiders. They build tangled, irregular webs in dark corners of buildings and hang upside down in them, vibrating rapidly when disturbed. Their fangs are small, but they are functional. The question people really want answered is whether cellar spider venom is secretly potent enough to harm a person but trapped behind fangs too short to penetrate skin.
A detailed study of the pholcid spider Physocyclus mexicanus tackled this directly by analyzing venom composition and testing its effects. The venom turned out to be genuinely complex, containing toxin proteins such as metalloproteases and neurotoxic peptides. In bioassays on crickets, the crude venom produced an effective paralytic dose comparable to that of other related spider taxa.
2PubMed Central. Not so Dangerous After All? Venom Composition and Potency of the Pholcid (Daddy Long-Leg) Spider Physocyclus mexicanusThat might sound alarming out of context, but paralytic potency against a cricket does not translate to danger for a human. The same research noted that documented bites on humans produce nothing more than a mild sting with no long-lasting effects. The researchers concluded bluntly that the effects of pholcid bites on humans and other mammals are “inconsequential.”3Frontiers in Ecology and Evolution. Not so Dangerous After All? Venom Composition and Potency of the Pholcid (Daddy Long-Leg) Spider Physocyclus mexicanus So cellar spiders can bite, their fangs can penetrate human skin, and their venom just is not dangerous to us. The myth gets every part of the story backward.
Where the Myth Came From
Nobody knows the exact origin of the “most venomous but can’t bite” claim, but a few factors probably fed it. The first is the identity confusion between harvestmen and cellar spiders. Harvestmen genuinely cannot bite in any meaningful way, and cellar spiders genuinely do have venom. Blend those two facts across two different animals sharing the same common name, and you get a story that sounds almost plausible: an animal with venom that cannot deliver it.
The second factor is how cellar spiders hunt. They are surprisingly effective predators of other spiders, including species much larger than themselves. Cellar spiders have been observed killing and eating black widows and other medically significant spiders. People who witnessed this probably assumed the cellar spider must have extremely potent venom to take down such dangerous prey. In reality, cellar spiders rely on their webs and their long legs to keep a safe distance while wrapping prey in silk. It is a matter of technique, not toxicity.
The myth persists in part because it is a great story. The idea of a humble, harmless-looking creature secretly carrying the deadliest venom on earth is compelling enough that people repeat it without checking. The television show MythBusters tested it on camera years ago, and venom researchers have addressed it repeatedly, but the claim continues to circulate.
How Harvestmen Actually Defend Themselves
Without venom, harvestmen rely on a completely different defensive toolkit. One of their most studied strategies is chemical defense. The neotropical harvestman Goniosoma longipes produces defensive secretions from scent glands that contain alkylated benzoquinones, the same class of irritant chemicals used by bombardier beetles. Testing showed these secretions successfully repelled seven species of ants, two species of large wandering spiders, and a frog species, though they did not deter an opossum.
4Journal of Chemical Ecology. Chemical Defense in Harvestmen (Arachnida, Opiliones): Do Benzoquinone Secretions Deter Invertebrate and Vertebrate Predators?Harvestmen also practice autotomy, the deliberate shedding of a leg to escape a predator’s grasp. Unlike some lizards that can regrow a lost tail, harvestmen never regenerate lost legs. Despite this permanent cost, the strategy appears worthwhile. Research on Prionostemma harvestmen showed that individuals with missing legs recovered normal locomotor performance quickly, compensating for the loss through changes in gait.
5PubMed Central. Rapid recovery of locomotor performance after leg loss in harvestmenAnother study found that male harvestmen with missing legs suffered no penalty in mating success, even though their courtship and mating behaviors require the use of legs.
6Behavioral Ecology and Sociobiology. Robustness in action: Leg loss does not affect mating success in male harvestmenSo harvestmen are far from defenseless. They just defend themselves through chemistry and sacrifice rather than through venom.
How Cellar Spiders Catch Their Prey
Cellar spiders build three-dimensional space webs made of an aerial tangle of silk lines with vertical threads descending to the ground. Some of these vertical lines are coated with sticky silk near the substrate, forming what researchers call gumfoot threads. These threads are spring-loaded and attached to the surface with a specially weakened silk anchor that detaches easily when something bumps into it, flinging the stuck prey upward into the web.
7PubMed Central. From fibres to adhesives: evolution of spider capture threads from web anchors by radical changes in silk gland functionThis engineering is worth appreciating because it explains how cellar spiders manage to catch prey that seems too big or too dangerous for them. A black widow wandering across a garage floor can blunder into a gumfoot thread, get yanked upward, and find itself tangled in a web where the cellar spider has the positional advantage. The cellar spider then throws additional silk from a safe distance using its long legs, immobilizing the prey before delivering a bite. The venom does not need to be especially powerful because the web does most of the work.
This hunting style is also why you find cellar spider webs in corners, basements, and garages rather than out in open air. They need a surface beneath their web for the gumfoot threads to anchor to, and they benefit from enclosed spaces that channel walking insects into their trap zone.
Poisonous Versus Venomous, and Why It Matters Here
Strictly speaking, the title question asks whether granddaddy long legs are “poisonous,” but what most people mean is “venomous.” The distinction is simple: a poisonous animal harms you if you eat or touch it, while a venomous animal harms you by injecting a toxin through a bite or sting. No granddaddy long legs of any type is dangerously venomous to humans. As for poisonous in the literal sense, harvestmen’s benzoquinone secretions are technically toxic chemical defenses, so you would not want to eat a handful of them, but this is roughly equivalent to the irritation you would get from handling a millipede. It is not the kind of danger anyone worries about in practice.
Spider Bite Misidentification Is a Bigger Problem
The granddaddy long legs myth is one piece of a broader pattern where people attribute medical problems to spiders that had nothing to do with them. Throughout the United States, skin wounds with tissue death are routinely diagnosed as brown recluse spider bites, even in areas where the brown recluse does not live. A review in the emergency medicine literature found that necrotic wounds caused by infections, cancers, and other processes were being misdiagnosed as spider bites, sometimes leading to delays in appropriate treatment and adverse outcomes.
8Annals of Emergency Medicine. The diagnosis of brown recluse spider bite is overused for dermonecrotic wounds of uncertain etiologyThe granddaddy long legs myth feeds into this culture of spider fear. If people believe a gangly, harmless creature is secretly the most dangerous spider on the planet, it reinforces the broader idea that spiders are sneaky threats lurking in every corner. In reality, the number of spider species in North America capable of causing medically significant bites is very small, and genuine spider bites are far less common than popular imagination suggests. When a mysterious skin lesion appears, the instinct to blame the nearest spider can actually cause harm by diverting attention from the real cause.
An Ancient Lineage That Predates the Dinosaurs
Harvestmen have been around for a remarkably long time. Fossils from the Late Carboniferous period, roughly 305 million years ago, show harvestmen that look essentially identical to modern species. Analysis of these fossils from Montceau-les-Mines in France concluded that harvestman body plans were established by that period and have remained largely unchanged ever since.
9Nature Communications. Anatomically modern Carboniferous harvestmen demonstrate early cladogenesis and stasis in OpilionesThat degree of evolutionary stability is unusual. Most animal groups have changed substantially over 300 million years. Harvestmen’s conserved body plan, combined with their low mobility compared to flying or fast-running animals, has made them a valuable model for studying biogeography. Because they do not disperse quickly over long distances, their distribution patterns often reflect ancient continental movements and climate shifts rather than recent colonization. For an animal most people dismiss as a creepy nuisance in the garden, harvestmen carry a deep and scientifically useful evolutionary history.
Their age also underscores a point about the venom myth. Harvestmen diverged from spiders hundreds of millions of years ago. They never had venom glands, and there is no evidence their ancestors did either. The claim that they possess spider-like venom is not just wrong about the present; it misunderstands their entire evolutionary lineage. These are animals that took a fundamentally different path from spiders early in arachnid history, one that never included venom as a strategy.