Daddy Longlegs Aren't (Necessarily) Spiders; So What Are They?

daddy-longlegs
The harvestman spider (Leiobunum rotundum) is often called a daddy longlegs, but so are a lot of other long-legged insect and non-insect species. Arterra/Universal Images Group/Getty Images

Here's one you might've heard before. Urban legend has it that daddy longlegs carry the most toxic venom of any known spider — but supposedly, their little fangs can't penetrate human skin. How convenient.

This belief has no basis in fact. Besides, "daddy longlegs" is just a colloquial name that's been applied to a wide range of unrelated animals. Most don't even qualify as spiders.

"Common names are troublesome," Rick Vetter tells us via email. A biologist and author, Vetter is an arachnid expert who's confronted plenty of misconceptions about spiders and their kin.

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Classification Station

"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 species name. These two-part names are internationally recognized — and each life form gets a combination that's totally unique.

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.

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The Harvestman Is Often Called Daddy Longlegs

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

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.

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.

Unable to produce silk, harvestmen don't build webs. 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.

Daddy longlegs
This Mitostoma chrysomelas, photographed in The Netherlands, is often mistakenly called a daddy longlegs.
Wikimedia Commons (CC BY 3.0)

"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.

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Some Flies Are Called Daddy Longlegs

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

Daddy longlegs
"Crane fly" is a common name referring to any member of the insect family Tipulida. In England and elsewhere, these are called daddy longlegs. See the problem with names?
Peakpx

Crane flies represent an insect order, the Tipulidae, that's more than 4,400 species strong. People tend to get them mixed up with 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.

Speaking of which...

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Cellar Dwellers, Too, Are Called Daddy Longlegs

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 spiders," these arachnids like dark habitats such as empty burrows, rocky crevices and of course, unkempt basements.

Daddy longlegs
This image shows a Pholcus phalangioides, also known as, yes, the Daddy longlegs.
Wikimedia Commons (CC BY-SA 2.5)

One species of European origin now shacks up in human dwellings all over the world. Pholcus phalangioides is a yellowish-brown predator that weaves horizontally oriented webs.

Pholcid fangs are tiny, only about 0.009 inch (0.25 millimeters) long — and they're designed to make physical contact with a corresponding spine to form pincers, not unlike a pair of tweezers.

It's true that pholcids are venomous, but the good news is 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 of the cellar spiders — is harmful to human beings.

Still, we may be on the cusp of something here. Pholcus phalangioides specializes in killing and devouring other spiders, including members of its own species. Who knows? Maybe those diet preferences gave rise to the nonsense rumors about super-toxic daddy longlegs venom.