The answer depends entirely on which creature you mean, because “daddy long legs” is a common name shared by at least three completely different animals. In most of the English-speaking world, the name refers to harvestmen, members of the order Opiliones, which are arachnids but definitively not spiders. In parts of the United States and Australia, the same name gets applied to cellar spiders (family Pholcidae), which are true spiders. And in the United Kingdom and Ireland, many people use “daddy long legs” for crane flies, which are not even arachnids but winged insects. The confusion has fueled one of the most persistent myths in popular biology and makes the question far more interesting than a simple yes or no.
Three Animals, One Nickname
The fact that a single common name applies to three unrelated animals is the root of almost every misconception about daddy long legs. Harvestmen, cellar spiders, and crane flies share little besides their gangly, long-legged appearance, and understanding which one someone is talking about clears up most of the confusion instantly.
Harvestmen are the group most people worldwide picture when they hear “daddy long legs.” They belong to the order Opiliones, a lineage of arachnids that split from spiders hundreds of millions of years ago. They have eight legs and share a class (Arachnida) with spiders, scorpions, ticks, and mites, but they sit on an entirely separate branch of that family tree. Calling a harvestman a spider is a bit like calling a fox a cat because both are furry mammals.
Cellar spiders, on the other hand, are genuinely spiders. They belong to the family Pholcidae, spin messy webs in basements and garages, and have all the standard spider equipment: fangs, venom glands, and silk. When Americans talk about a “daddy long legs” dangling in the corner of a room, they often mean one of these. Crane flies are the odd one out entirely. They are delicate, mosquito-like insects with six legs and wings, commonly seen bumbling around porch lights on summer evenings. They belong to a completely different part of the animal kingdom.
How Harvestmen Differ from True Spiders
Because harvestmen are the animal most often at the center of the “is it a spider?” debate, it helps to know exactly where they diverge from spiders anatomically. The differences are substantial and visible to the naked eye once you know what to look for.
A spider’s body is divided into two clearly distinct segments: a front section (the cephalothorax) and a rear section (the abdomen), connected by a narrow waist called a pedicel. A harvestman’s body looks like a single compact oval. The two segments are fused broadly together, giving the animal a pill-shaped or rounded appearance with no visible waist. This is often the easiest way to tell them apart at a glance.
Spiders almost always have eight eyes, sometimes six, arranged in species-specific patterns across the front of the head. Harvestmen have at most a single pair of simple eyes mounted on a small turret on top of the body. Recent research has revealed something unexpected about those eyes: extant harvestmen actually retain two additional pairs of vestigial eyes that never fully develop. Researchers found that embryonic harvestmen express light-sensitive genes in median and lateral cell groups that correspond to the locations of ancestral eyes, even though those structures do not form functional organs in the adult animal.1Cell Press (Current Biology). Vestigial eyes in daddy-longlegs and the phylogeny of fossil harvestmen The finding suggests harvestmen descended from ancestors with more complex visual systems and gradually lost them over evolutionary time.
Two other critical differences: spiders produce silk from spinnerets and use venom delivered through fangs to subdue prey. Harvestmen have neither silk glands nor venom glands. They cannot spin webs, and they cannot deliver a venomous bite. This distinction feeds directly into one of the most famous myths about them.
The “Most Venomous” Myth, Debunked
You have probably heard some version of this claim: daddy long legs are the most venomous creatures in the world, but their fangs are too small to pierce human skin. It is one of those factoids that gets passed around so confidently that many people treat it as settled science. In reality, it falls apart on inspection for both animals the name commonly refers to.
For harvestmen, the myth is nonsensical on its face. Harvestmen have no venom glands at all. They do not produce venom of any kind, potent or otherwise. They physically cannot envenomate anything, and their mouthparts are designed for chewing decomposing matter and small prey, not for piercing skin. There is no venom to test because none exists.
For cellar spiders (Pholcidae), the myth at least has the right starting point: these are real spiders that do possess venom. But the claim that their venom is extraordinarily dangerous has been directly tested and found to be wrong. A study on the pholcid spider Physocyclus mexicanus analyzed both the composition of its venom and its effects on living targets. In insect bioassays, the venom’s potency was comparable to that of other small spider species in the same broad group. More importantly, documented bites on humans produced nothing more than a mild sting with no lasting effects.2Frontiers in Ecology and Evolution. Not so Dangerous After All? Venom Composition and Potency of the Pholcid (Daddy Long-Leg) Spider Physocyclus mexicanus The researchers concluded bluntly that the effects of pholcid bites on humans and other mammals are “inconsequential.”
So the myth fails twice over. The animal most commonly called a daddy long legs has no venom at all, and the spider that sometimes shares the name has venom that is weak and medically insignificant to humans. Nobody has identified the origin of this urban legend, but it persists with remarkable tenacity regardless.
What Harvestmen Actually Eat
Without venom or silk, harvestmen have to get their meals a different way. They are generalist feeders: part scavenger, part opportunistic predator. Their diet is surprisingly broad and includes both living prey and dead organic matter, which makes them more ecologically versatile than most spiders.
Field studies of harvestmen in New Zealand documented them catching and eating a wide range of invertebrates, including earthworms, amphipods, beetles, flies, moths, cockroaches, and even other arachnids, including other harvestmen. Individuals of both sexes were able to capture and subdue live prey as large as themselves despite having no venom or silk to help.3BioOne Complete. Diet, predators, and defensive behaviors of New Zealand harvestmen (Opiliones: Neopilionidae) They simply grab prey with their pedipalps (the small appendages near the mouth) and chew.
Harvestmen also readily scavenge, feeding on dead insects, decaying plant material, bird droppings, and fungi. This dietary flexibility is part of what makes them so successful. They fill an ecological niche closer to that of a tiny omnivorous scavenger than to the ambush-predator role spiders typically occupy. You will find them in leaf litter, under logs, in garden beds, and on tree trunks, basically anywhere there is damp organic material and small invertebrates.
Chemical Warfare and Detachable Legs
Without venom or the ability to spin a retreat, harvestmen have evolved other ways to avoid being eaten. Their two most distinctive defense strategies are chemical secretions and deliberate leg loss.
Many harvestmen species have scent glands on the front of their bodies that can spray a foul-smelling chemical mixture when the animal is disturbed. In one well-studied European species, Rilaena triangularis, the secretion is ejected as a directed jet and contains mainly 1,4-benzoquinone along with 1,4-naphthoquinone and caprylic acid.4PubMed Central. Benzoquinones from scent glands of phalangiid harvestmen (Arachnida, Opiliones, Eupnoi): a lesson from Rilaena triangularis Benzoquinones are irritating, pungent compounds that deter predators ranging from ants to birds. If you have ever picked up a harvestman and noticed a sharp, unpleasant smell on your fingers, that is the defense system at work.
The other well-known trick is autotomy, the ability to shed a leg on purpose. When a predator grabs a harvestman by one of its long legs, the leg can detach at a predetermined breakpoint. The severed leg keeps twitching for minutes, which may distract the attacker long enough for the harvestman to escape. Unlike lizards that regrow their tails, harvestmen never regenerate lost legs.5Behavioral Ecology and Sociobiology. Robustness in action: Leg loss does not affect mating success in male harvestmen
You might expect losing a leg to be a serious handicap, and it would seem especially costly for an animal that uses its extraordinarily long second pair of legs as sensory feelers, sweeping them ahead like antennae to navigate its environment. But research tracking harvestmen before and after leg loss found that they recovered their normal speed and acceleration remarkably quickly. Whether they lost locomotor legs or sensory legs, the animals showed no lasting decline in movement performance.6Nature Publishing Group. Rapid recovery of locomotor performance after leg loss in harvestmen Leg loss is evidently a routine event in a harvestman’s life, and the cost of sacrificing a limb is low enough that it remains a viable survival strategy.
An Ancient Lineage
Harvestmen are not just separate from spiders taxonomically; the two groups have been on independent evolutionary paths for an enormous stretch of time. The fossil record for Opiliones extends back to the Early Devonian period, roughly 410 million years ago, making harvestmen one of the oldest known groups of land-dwelling arachnids. Their major lineages had already diversified by the Carboniferous period, well over 300 million years ago.7Royal Society Publishing. The Opiliones tree of life: shedding light on harvestmen relationships through transcriptomics
The order includes four living suborders that differ dramatically from one another. What most people in temperate regions recognize as “daddy long legs,” the leggy, fast-moving creatures found under rocks and in garages, belong to the suborder Eupnoi. But the order also includes the tiny, mite-like Cyphophthalmi, the ornate Dyspnoi, and the heavily armored Laniatores, some of which look more like miniature beetles than anything you would associate with the daddy-long-legs image. With over 6,600 described species worldwide, Opiliones are a diverse order in their own right, not a footnote to spiders.
Ancient Devonian fossils of harvestmen are strikingly similar to modern forms, suggesting their basic body plan has been stable for hundreds of millions of years. The vestigial eyes discovered in embryonic harvestmen offer a window into what their ancestors may have looked like: animals with three pairs of functional eyes, a visual system that was gradually pared down as these creatures adapted to life in dim, damp microhabitats where keen eyesight mattered less than chemical sensing and touch.
Reproduction and Fatherly Devotion
Harvestmen reproduce in ways that set them sharply apart from spiders. In most spider species, the male transfers sperm indirectly, using modified pedipalps to deposit a sperm packet into the female. Harvestmen are unusual among arachnids in that the male has an actual penis and inseminates the female directly during face-to-face mating. During courtship in one well-studied group, the male grasps the female with his pedipalps, everts his penis, and offers a nuptial gift from accessory glands near his pregenital opening before copulation.8Public Library of Science (PLOS ONE). Comparative Analyses of Reproductive Structures in Harvestmen (Opiliones) Reveal Multiple Transitions from Courtship to Precopulatory Antagonism The nuptial gift appears to play a role in convincing the female to accept mating, though the specifics vary among species.
What happens after mating is where things get genuinely surprising. In many arachnid species, parental care is rare, and when it occurs, it is usually the female who guards the eggs. Several harvestman species flip that script completely. In the tropical harvestman Zygopachylus albomarginis, males build, maintain, or take over small mud nests, and then guard the eggs deposited inside them. The fathers remove fungus, repair damage to the nest structure, and defend the eggs from ants and other harvestmen.9Animal Behaviour. Paternal care in a neotropical harvestman, Zygopachylus albomarginis (Arachnida, Opiliones: Gonyleptidae)
In other neotropical species, the pattern is similar: females lay eggs in natural cavities or sheltered sites, then leave. Males take over all postzygotic care, protecting eggs and nymphs from predators until the young disperse.10Animal Behaviour. Mating system and exclusive postzygotic paternal care in a Neotropical harvestman (Arachnida: Opiliones) Exclusive paternal care is rare across the animal kingdom and extremely unusual among arachnids, making harvestmen a fascinating study system for researchers interested in the evolution of parental behavior.
Cellar Spiders and the Brown Recluse Connection
While harvestmen are the daddy long legs found outdoors in gardens and forests, the creature most people encounter indoors under that name is usually a cellar spider. Pholcids are genuine spiders, complete with eight eyes (sometimes six), a two-part body, silk, and venom glands. They build loose, irregular webs in corners, cellars, and garages, and hang upside down, vibrating rapidly when disturbed to blur their outline and confuse predators.
Cellar spiders have gained a quiet reputation as beneficial household residents because of their tendency to prey on other spiders. In at least one documented case in central Illinois, cellar spiders were actually purchased and deliberately released inside a building in an attempt to control brown recluse spider populations.11The Great Lakes Entomologist. Coming Soon to a Cellar Near You: Novel Range Expansion of a Short-Bodied Cellar Spider, Physocyclus enaulus (Araneae: Pholcidae), in a Building in Central Illinois, USA Whether this strategy works reliably is debatable, but it reflects the general perception that pholcids are harmless to humans and potentially useful roommates. Their webs are admittedly messy, though, and heavy infestations can make a basement look neglected in a hurry.
If you are trying to figure out which “daddy long legs” you are looking at in your home, the key features are straightforward. A cellar spider has a visible two-part body, hangs in a web, and moves with the deliberate, slightly jerky gait of a web-dwelling spider. A harvestman has a compact one-piece body, no web, and tends to scuttle quickly across surfaces. If the animal has wings, it is a crane fly, and it has no interest in your basement. It is just lost.
Aggregation Behavior
One of the most visually striking things harvestmen do is gather in large clusters, sometimes numbering in the hundreds or even thousands. You may have seen photos or videos of what looks like a pulsating ball of legs clinging to a tree trunk, cave wall, or the underside of a bridge. These aggregations are not mating events or family groups. They are primarily thought to serve thermoregulatory and humidity-retention purposes: by huddling together in a sheltered spot, the animals collectively reduce water loss and buffer temperature extremes.
There is likely a predator-deterrence component as well. A tightly packed mass of harvestmen, all bobbing up and down in unison when disturbed, can look like a single much larger organism, and the combined chemical secretions from hundreds of scent glands create a potent deterrent cloud. Aggregations tend to form in cool, damp, sheltered locations and are most common in late summer and autumn when harvestmen populations are at their peak. Despite the unnerving appearance, the clusters are completely harmless. The animals are not nesting, breeding, or preparing to invade your home. They are just staying moist and safe.
These gatherings underscore how different harvestmen are from spiders in their social tendencies. Most spider species are territorial loners that will eat a conspecific as readily as they will eat a fly. Harvestmen, by contrast, tolerate and even seek out the company of their own kind, an unusual trait for arachnids and one more reason they deserve recognition as their own distinct group rather than being lumped in as “a type of spider.”