Are Daddy Longlegs Truly Spiders? Setting the Record Straight

"Red-backed salamander," "shortleaf pine tree" and "pygmy sperm whale" are all examples of common names. They're the catchy, popular labels most of us use when we talk about living things in an informal setting.

Sometimes, they're region-specific. When you're above the Mason-Dixon Line, saying "crawdad" instead of "crayfish" might raise a few eyebrows. Likewise, the American woodcock is variously called the "timberdoodle," the "Labrador twister" and the "bogsucker."

Scientific names work differently.

Under the system of binomial nomenclature, every organism receives a (capitalized) genus name followed by a (lowercase) species name. These two-part names are internationally recognized, and each life form gets a combination that's totally unique, making animal classification much clearer.

By the same token, a single organism cannot have multiple scientific names. That's a big no-no. So although the American woodcock collects common names like they're Pokemon cards, it's only got one scientific name: Scolopax minor.

As common names go, "daddy longlegs" is overused. And it's pretty inconsistent.

The name "daddy longlegs" (sometimes styled as "daddy long legs") comes from the appearance of these creatures, characterized by their long, slender legs. The term "daddy" is a familiar and affectionate term, often used in a playful manner — though, these insects don't necessarily conjure feelings of playfulness and affection.

Usually, when Americans say it, they're referring to one of the 6,000-plus arachnid species within the order Opiliones. Some folks know these critters as the "harvestman."

But whatever you do, don't call them "spiders." Tarantulas, black widows and other genuine spiders belong to a different order altogether (order Araneae).

Look at a spider and you'll see two main body segments that are clearly distinguishable: The cephalothorax (where the head resides) and the abdomen. On harvestmen, these components are fused, giving the body an oval-like appearance. And whereas spiders possess eight eyes apiece, harvestmen only have two.

Unlike true spiders, harvestmen lack venom glands, fangs and the ability to produce silk. However, as a 2014 study in the Journal of Experimental Biology reported, the species Mitostoma chrysomelas uses natural adhesives on its legs to capture wriggling victims.

"Except for one weird family, all spiders have venom to subdue prey. Harvestmen have no venom," Vetter says. So let the record show: They're not dangerous to people. You can breathe easy around these daddy longlegs.

Instead of envenomating other animals, harvestmen rip their meals apart with appendages located near the mouth. Slugs, springtails and earthworms are just some of the invertebrates these creatures will hunt; they're not too picky and don't mind scavenging once in a while.

Harvestmen may not be spiders, but at least they're arachnids. "In Great Britain," Vetter notes, the name daddy longlegs "refers to ... crane flies."

Those happen to be insects. You can tell because spiders, huntsmen and other arachnids walk around on four pairs of legs, whereas crane flies only have three pairs. Coincidentally, all insects possess three main body segments (plus a set of antennae).

Crane flies represent an insect order, the Tipulidae, that's more than 4,400 species strong. People tend to get them mixed up with large mosquitoes, but these flies don't suck blood. They spend most of their lives as water- or soil-based larvae. Once that phase ends, the invertebrates mature into two-winged adults.

Brits don't call them "daddy longlegs" for nothing. Just as advertised, mature crane flies do, in fact, have noticeably long legs. Sometimes, these appendages are twice the length of the insect's body. According to the Entomological Society of America, the biggest known crane fly displays a 10-inch (25.4-centimeter) leg span.

Adults don't tend to have big appetites; certain species will stop eating altogether after the larval stage. Nevertheless, crane flies provide an important food source for other animals, including reptiles, birds and spiders.

Part of the family Tetragnathidae, these spiders are often mistaken for daddy longlegs, due to their long, thin legs and delicate appearance. However, these creatures have distinct characteristics and behaviors that set them apart.

Unlike the harvestman, which lacks the ability to spin webs, long-jawed orb weavers are expert web builders. Found near water sources like rivers, lakes and wetlands, this spider species construct intricate orb-shaped webs to capture their prey. Their webs are strategically placed to maximize their hunting efficiency, targeting flying insects.

One of the most notable features of long-jawed orb weavers is their elongated chelicerae (jaws), which they use to grasp and subdue their prey. They also have distinct body segments, unlike the fused bodies of harvestmen.

Despite being confused with venomous spiders, long-jawed orb weavers are harmless to humans. They possess short fangs and lack the potent venom of spiders like the brown recluse.

Active primarily during the evening and nighttime, long-jawed orb weavers contribute significantly to maintaining ecological balance by preying on insects. Their presence near water provides a vital food source for birds and amphibians.

In a surprise twist, some people reserve the common name "daddy longlegs" for (drumroll!) a group of actual spiders. Ladies and gentlemen, it's high time we introduced the Pholcidae.

Better known as the "cellar spider" or skull spider (due to its massive cranium), this arachnid likes dark habitats such as empty burrows, rocky crevices and, of course, unkempt basements.

One species of European origin can now be commonly found shacking up in human dwellings all over the world. Pholcus phalangioides is a yellowish-brown predator that weaves horizontally oriented webs. Another member of this family, the marbled cellar spider (Holocnemus pluchei), is similarly adept at occupying human spaces.

Pholcid fangs are tiny, only about 0.009 inches (0.25 millimeters) long — and they're designed to make physical contact with a corresponding spine to form pincers, functioning almost like a pair of tweezers.

It's true that pholcid spiders are venomous, but the good news is its venoms don't affect all targets equally. When researchers examined the venom of a pholcid called Physocyclus mexicanus in 2019, they found it was extremely hazardous to insects. Yet the creature's bite had an "inconsequential" effect on mammals.

There's simply no evidence that this arachnid — or any cellar spider — is harmful to human beings.

Interestingly, Pholcus phalangioides specializes in killing and devouring other spiders, including members of its own species. Many Pholcid spiders, including Pholcus phalangioides, exhibit a behavior known as "web-bouncing" or "vibrating" when threatened. This rapid shaking of their webs makes it difficult for predators to locate them accurately.

This predatory behavior and defense mechanism might have contributed to the myths about super-toxic daddy longlegs venom. However, rest assured, these spiders pose no threat to humans and, in reality, play a beneficial role in controlling pest populations.

Brown recluses (Loxosceles reclusa) and daddy longlegs spiders (specifically cellar spiders) share some quirky similarities, despite their differences. Both enjoy the cozy, dark corners of basements, attics and closets, making your storage spaces their favorite hangouts. These night owls come alive once the sun sets, heading out on the hunt for tasty insects.

While both use venom to subdue their prey, only the brown recluse packs a punch potent enough to cause significant reactions in humans (but even then, they rarely actually induce those reactions).

As mentioned earlier, cellar spiders vibrate rapidly in their webs to confuse predators, a trick that most spiders, including the brown recluse, don't have up their sleeve. Instead, brown recluses rely on their stronger muscles and agility to capture prey and evade threats.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.