According to urban legend, daddy long-legs produce the most potent venom of any spider, but their fangs aren’t strong enough to penetrate human skin. This isn’t true.
The name "daddy long-legs" is used to refer to several species, including some spiders, but none of them are particularly venomous. When you think of "daddy long-legs," you’re probably thinking of one of these creatures:
- Pholcidae - Spiders in the Pholcidae family are found throughout the world, and they frequently build their messy webs in attics, crawlspaces, and other undisturbed areas. They’re also known as cellar spiders.
Pholcidae are not dangerous to humans. Their fangs are short, but capable of penetrating human skin. A 2019 study published in Frontiers in Ecology and Evolution found that the "effects of bites on humans and other mammals are inconsequential."
However, Pholcidae seem to have different peptides and proteins than those found in other spiders' venom; this could explain why Pholcidae regularly prey on spiders that are far more dangerous to mammals. Some Pholcidae, for instance, prey on spiders in the Black Widow family.
That’s one possible explanation for the myth—someone saw a Pholcidae preying on a dangerous spider, and incorrectly assumed that this meant the Pholcidae was more dangerous to humans. Alas, nature doesn’t really work that way.
"Documented bites on humans make clear that while these spiders can bite, the typical result is a mild sting with no long-lasting effects," the study’s authors wrote.
Of course, ethical issues prevent scientists from subjecting people to spider bites, so most of what we know about Pholcidae bites comes from chemical analyses and anecdotal evidence. One such piece of evidence: In a 2004 episode of the Discovery Channel show Mythbusters, host Adam Savage intentionally agitated one of the spiders and was bitten; he reported a mild burning sensation that lasted a few seconds.
- Harvestmen - This common name refers to Opiliones, an order of scavenger arachnids found worldwide. They’re frequently found in damp, undisturbed areas, but they do not build webs. Opiliones have eight long legs, but they’re not technically spiders. They have no venom glands of any kind.
Harvestmen do not have fangs; instead, they have chelicerae, which they use to grasp their food. On most species, these appendages are small and not capable of breaking human skin.
- Crane Flies - These insects are certainly the outlier on this list; they’re not spiders, and they don’t look anything like spiders. They have six legs, wings, and an adult lifespan of about 10 to 15 days.
Crane flies don’t have jaws or venom, so they’re completely harmless to humans. In some parts of the world, their larvae is considered a delicacy.
In case you’re curious, the most venomous spider in the world is probably Atrax robustus, according to Guinness World Records, which defines “most venomous" as “most toxic to humans.” Atrax robustus is better known as the Sydney funnel-web spider, and it’s native to Australia (where else?).
For primates unlucky enough to suffer a bite, 0.2 milligrams of venom per kilogram of body weight is a fatal dose. The good news: There’s an effective antivenom, and no fatalities have been recorded since the antivenom’s introduction.