Are Daddy Long Legs Scorpions or Spiders?

The creatures most commonly called “daddy long legs” are harvestmen, members of the arachnid order Opiliones, and they are neither scorpions nor spiders. They belong to their own ancient lineage that split from other arachnid groups hundreds of millions of years ago. The confusion is understandable because the name “daddy long legs” gets applied to at least three completely different animals depending on where you live, and all three happen to be leggy and small. Sorting out which creature is which reveals some genuinely surprising biology.

Three Animals, One Nickname

The name “daddy long legs” is one of the most ambiguous common names in the English-speaking world. In most of the United States, Canada, and the United Kingdom, it refers to harvestmen, the round-bodied arachnids you see bobbing across garden walls and forest floors on impossibly thin legs. In parts of the southern U.S. and Australia, the same name gets applied to cellar spiders in the family Pholcidae, the wispy spiders that build messy webs in corners and basements. And in the UK and Ireland, “daddy long legs” also refers to crane flies, those gangly, mosquito-looking insects that blunder into houses in autumn. A crane fly is not even an arachnid. It has wings, six legs, and belongs to the fly order Diptera.

This article focuses mainly on harvestmen, since they are the most widespread bearers of the name and the ones that generate the most identity confusion. But the cellar spider overlap matters too, especially when it comes to the famous venom myth, which we will get to shortly.

Why Harvestmen Are Not Spiders

Harvestmen and spiders are both arachnids, which means they share a broad family tree with scorpions, ticks, and mites. But calling a harvestman a spider is like calling a cat a dog because they are both mammals. The two orders diverged a very long time ago, and the anatomical differences are substantial.

The most obvious difference is body shape. Spiders have two clearly distinct body segments joined by a narrow waist: a front section (the cephalothorax) and a rear section (the abdomen). In harvestmen, those two sections are fused into what looks like a single compact oval or pill-shaped body. There is a joint between them, but it is broadly joined, so harvestmen appear to be all one piece with legs stuck on.

Spiders produce silk from spinnerets on their abdomens. Harvestmen have no silk glands and build no webs. Spiders have venom glands connected to their fangs and use venom to subdue prey. Harvestmen have no venom glands at all. They eat by grasping food with their pedipalps and chelicerae (mouthparts) and chewing it directly, sometimes scavenging dead material, sometimes catching tiny invertebrates. They can handle solid food, unlike spiders, which must liquefy their meals externally.

Eyes tell a different story too. Most spiders have eight eyes arranged in species-specific patterns. Harvestmen typically have just two eyes, mounted on a raised bump called an ocularium near the top of the body. Research on chelicerate visual systems has shown that arachnids in general can have two types of eyes, median (principal) and lateral (secondary), which differ in how they develop and connect to the brain.¹ Harvestmen possess only median eyes, and recent work has revealed that some species retain vestigial lateral eye tissue, suggesting their ancestors may have had more complex vision that was lost over evolutionary time.

Then there is breathing. Spiders breathe through structures called book lungs, flat plates stacked like pages in a book inside the abdomen. Harvestmen breathe through tracheae, a system of branching tubes that deliver air directly to tissues, more similar to the way insects breathe. Fossils from the 400-million-year-old Rhynie cherts of Scotland preserve harvestman tracheal tubes in extraordinary detail, providing the oldest unequivocal evidence of tracheal air-breathing in any arthropod.²

Why Harvestmen Are Not Scorpions

The scorpion comparison comes up less often, but it surfaces because scorpions are the other arachnid order most people can name, and someone encountering an unfamiliar eight-legged creature might wonder. Harvestmen and scorpions are about as different as two arachnids can be. Scorpions have a segmented tail ending in a venomous stinger, large pincerlike pedipalps, and a flattened body built for desert life. Harvestmen have none of these features. Their pedipalps are small and leglike, they have no tail, no stinger, and no venom.

Phylogenomic analyses placing Opiliones within the broader arachnid family tree have confirmed that harvestmen form a well-supported group distinct from scorpions and spiders alike.³ The exact branching order among arachnid groups is still debated, and different studies shuffle the relationships depending on which genes or fossils are analyzed. What is not debated is that Opiliones is its own order. Harvestmen are no closer to scorpions than they are to ticks.

The Venom Myth

You have almost certainly heard this one: “Daddy long legs are the most venomous creatures in the world, but their fangs are too small to bite you.” This is wrong on every level, but it persists partly because the name “daddy long legs” blurs two different animals together.

Harvestmen, the true daddy long legs in most of the world, have no venom whatsoever. They cannot bite you in any meaningful sense. They lack venom glands, full stop. The myth does not even get off the ground if you are talking about harvestmen.

Cellar spiders, the other “daddy long legs,” do have venom glands and fangs and can technically bite. But research on the pholcid spider Physocyclus mexicanus found that their venom, while containing some interesting peptides, produces nothing worse than a mild sting in humans, with no lasting effects.⁴ Their fangs are also not too small to penetrate human skin. The whole premise of the myth is fabricated. Cellar spiders can bite, the bite is trivial, and their venom is unremarkable in potency. No version of “daddy long legs” is secretly harboring the world’s deadliest venom.

How Harvestmen Defend Themselves Without Venom

If harvestmen cannot bite or sting, how do they avoid being eaten? They have a chemical defense system that is more sophisticated than you might expect from something that looks like a walking lentil on stilts.

Harvestmen possess scent glands, sometimes called defensive glands or ozopores, located on the front part of their body. When disturbed, many species release a pungent secretion that repels predators. The chemistry varies across species but frequently involves benzoquinones, the same class of irritating compounds that bombardier beetles are famous for. In the harvestman Rilaena triangularis, the secretion contains mainly 1,4-benzoquinone along with 1,4-naphthoquinone and octanoic acid, and the animal can aim a directed jet at a threat.⁵

Experimental work on the neotropical harvestman Goniosoma longipes showed that its benzoquinone secretion repelled seven species of ants, two species of large wandering spiders, and a frog species, keeping predatory ants at bay for at least ten minutes. The defense was not universal, though. An opossum was not deterred.⁶ So the chemical shield works well against arthropod predators and some vertebrates, but a determined mammal can power through it.

Some harvestmen go further. An undetermined species of Prionostemma from Costa Rica was found to include myrmicacin, a compound normally associated with leaf-cutter ants, in its scent gland secretion. The evidence suggests this species sequesters the compound from ants it eats, effectively recycling a predator’s own chemistry for self-defense.⁷ Most harvestman defensive secretions were assumed to be produced by the animal’s own biochemistry, so finding sequestration was unexpected.

Beyond chemistry, harvestmen also famously shed legs when grabbed. A detached leg can keep twitching for seconds or minutes, distracting the predator while the harvestman escapes. Unlike some spiders and crabs, harvestmen cannot regenerate lost legs, so the sacrifice is permanent. Leg loss is common enough in wild populations that finding a harvestman running on seven or even six legs is not unusual.

A Remarkably Ancient Lineage

Harvestmen are old. The Rhynie chert fossils from Scotland, dating to roughly 400 million years ago in the Devonian period, preserve harvestmen that are strikingly modern in overall appearance. Those fossils include both male and female reproductive structures and branching tracheal tubes, meaning harvestmen had already evolved their characteristic body plan and breathing system by the time the first forests were just beginning to appear on land.² For comparison, the earliest definitive spiders appear in the fossil record somewhat later, and modern-looking spider groups diversified mainly in the Mesozoic.

The fact that 400-million-year-old harvestmen already looked recognizably like today’s daddy long legs speaks to remarkable evolutionary conservatism. The basic formula of a compact fused body, long legs, tracheal breathing, and direct mating has apparently worked well enough that natural selection has not remodeled it in any dramatic way over hundreds of millions of years.

Unusual Reproductive Biology

One of the more surprising differences between harvestmen and other arachnids is that male harvestmen have a penis. This is genuinely unusual among arachnids. Male spiders transfer sperm using modified pedipalps, essentially loading sperm onto what are effectively specialized leg-appendages and inserting them into the female. Scorpions deposit a spermatophore on the ground and guide the female over it. Harvestmen have direct copulation with an intromittent organ, and females have a corresponding ovipositor for laying eggs, a tube-like structure they use to probe suitable egg-laying sites and deposit eggs into soil or crevices.

The diversity of genital structures across the major harvestman subgroups is striking. In one group, the males have a needle-like stylus that enters the female’s sperm storage organs directly. In another, the stylus does not fit the storage organs, and sperm is released into the ovipositor’s main channel, meaning the female likely controls whether and how sperm reaches storage. In a third group, the male genitalia are complex enough that researchers believe they serve multiple mechanical functions at once: fastening, intromission, and opening internal structures to allow sperm release.⁸ This variation in genital anatomy across harvestman lineages has become a major research area, partly because it offers insights into how female choice and sperm competition operate in animals with direct copulation.

Fathers That Guard Eggs

Harvestmen also break the arachnid mold when it comes to parental care. In many arachnid species, the female does all the egg-guarding if there is any parental care at all. Some harvestman species flip this entirely: the male guards the eggs. In certain neotropical species, males defend egg clutches deposited on their territory, sometimes tending eggs from multiple females simultaneously.

This arrangement comes at a cost. Research on paternal care in a neotropical harvestman found that caring males foraged less frequently than non-caring individuals and their body condition deteriorated over the course of the guarding period. The tradeoff, however, was not as severe as you might expect: caring males did not show lower survival rates compared to non-caring males and females.⁹ So guarding eggs means eating less and losing weight, but it does not seem to shorten the father’s life. The payoff, presumably, is that more of his offspring survive.

Exclusive paternal care is rare across the animal kingdom and essentially unheard of in spiders and scorpions. Its presence in harvestmen is one more reminder that despite the superficial resemblance of “small arachnid with long legs,” harvestmen are doing their own thing evolutionarily.

How to Tell Them Apart at a Glance

If you find a leggy creature in your house or garden and want to know which “daddy long legs” you are looking at, a few quick observations will sort it out:

Harvestman: Compact, pill-shaped body with no visible waist. No web. Two eyes on a central bump. Found wandering on walls, fences, leaf litter, or tree trunks. If you touch it, it may bob rapidly up and down or release a faintly acrid smell.
Cellar spider: Small body with a distinct waist between cephalothorax and abdomen. Hangs upside-down in a loose, messy web, usually in a corner or basement. When disturbed in its web, it vibrates rapidly, becoming a blur.
Crane fly: Has wings, six legs, and a long slender abdomen. Flies clumsily and is attracted to lights. Clearly an insect, not an arachnid. Common in late summer and autumn.

Harvestmen are also often seen in aggregations. In cool weather or sheltered spots, dozens or even hundreds may cluster together in a slowly writhing mass on a tree trunk or cave wall. The reasons for this aggregation behavior are not fully settled, but thermoregulation and predator dilution are the leading hypotheses. Spiders rarely aggregate outside of communal web-building species, and crane flies do not cluster in the same way.

The Body Plan That Diversified Quietly

Because harvestmen look so uniform at first glance, it is easy to assume there is not much variety in the group. In fact, there are over 6,600 described species of harvestmen worldwide, and the actual number is certainly higher since many tropical species have not been formally named. They range from the familiar long-legged species of temperate gardens to short-legged, armored tropical forms that look more like beetles than the stereotypical daddy long legs.

Research on how body segments are patterned during development in harvestmen has shown that the same toolkit of genes responsible for body-segment identity in spiders and other arthropods is deployed differently in Opiliones, contributing to the distinctive fused body plan.¹⁰ In other words, harvestmen have the same genetic instructions as spiders for making body segments, but they read those instructions differently, which is part of why their bodies ended up looking so different despite sharing a common arachnid ancestor.

Some of the most visually dramatic harvestmen live in the tropics. Species in the suborder Laniatores can have armored bodies covered in spines, bright warning colors, and legs that are short and stout rather than the threadlike limbs northerners associate with the group. If someone showed you a photograph of a spiny, iridescent-green Laniatorean harvestman from Brazil, you would not immediately connect it to the drab brown creature wobbling across your porch in September. Yet genetically, they are all Opiliones, unified by the same core traits of fused bodies, tracheal breathing, direct mating, and no venom.