The Myth About Daddy Longlegs You Shouldn't Believe

There is a popular animal "fun fact" that says daddy longlegs are the most venomous spiders in the world, and the only reason they don't kill humans is that their fangs are too small to penetrate our skin, but this isn't the case at all. In fact, many people who eagerly share this fact don't even know what animal they are talking about. Daddy longlegs isn't a scientific term, but it is colloquially used to refer to no fewer than three different species, only one of which is actually a spider.

The only true spiders that go by daddy longlegs are pholcid spiders, more commonly known as cellar spiders. Otherwise, the term is often used for crane flies, which are insects in the family Tipulidae, with extremely long legs that are often mistaken for both pholcid spiders and mosquitos. In fact, it's also called a mosquito hawk by some, only further confusing the species' nomenclature.

Crane flies are easy to distinguish once they spread their wings, but the third species that bears the daddy longlegs title is more deceptive. They are wingless arachnids, but they aren't spiders. Rather, they belong to an order called Opiliones, and are also known as harvestmen. They differ from spiders in that they only have one body segment and two eyes, and crucially, they lack venom glands. The same is true for crane flies, so two of the three creatures we call daddy longlegs don't even make venom. As for the actual spiders, it's a bit more complicated.

The only true spiders to bear the name daddy longlegs are members of the family Pholcidae, also known as pholcid spiders or cellar spiders. There are nearly 2,000 different species of pholcid spiders, all characterized by their extremely long legs. These lengthy appendages serve a useful purpose, as the spiders can use their hind legs to hurl silk at prey, capturing victims much larger than themselves while keeping their bodies away from potential danger. The legs also help pholcid spiders to move quickly across different surfaces and to sense vibrations to locate potential prey.

Pholcid spiders are venomous, but so is nearly every other spider (there are only two non-venomous spider groups), and their venom is targeted at the creatures they prey on, not human beings. Pholcid spiders are toxic to the flies and bees they eat, but their venom is not strong enough to harm a human. Furthermore, their jaws really aren't strong enough to pierce our skin, so that part of the legend actually is true. A 2019 study published in the journal Frontiers in Ecology and Evolution compared the venoms of the pholcid spider Physocyclus mexicanus with the western black widow (Latrodectus hesperus) when injected into mice, and found that the black widow's venom was more toxic. Still, even that can't come close to the danger of the actual most venomous spider in the world.

The real champions of arachnid toxicity come from Australia, a land that seems positively brimming with venomous species that can kill you in minutes. Australian funnel-web spiders, which comprise the family Atracidae, are believed to be the most venomous spiders in existence, named for the funnel-shaped webs they build to pull passing prey into. The Sydney funnel-web spider (Atrax robustus) is particularly notorious due to its presence around Australia's most populous city. There were 13 recorded deaths from Sydney funnel-web bites prior to the introduction of antivenom in 1981, and although no deaths have occurred since, the highly aggressive funnel-web spiders still bite 30–40 people on a yearly basis.

Considering both the deadly record of the funnel-web spider and its intimidating appearance, it's hard to imagine how the spindly daddy longlegs was ever thought to be more dangerous, but one potential explanation may lie in yet another spider. Brown recluse spiders of the genus Loxoceles are not the most venomous spiders in the world, but they are possibly the most venomous in the United States, rivalled only by black widows. Brown recluses have a very similar appearance to pholcid spiders, with long spindly legs. However, you can identify a brown recluse by its body size and other unique features. Brown recluses are widespread in the U.S., but fortunately, they live up to their name, and only bite people if they are provoked.