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There is a widespread claim that daddy longlegs are the most venomous spiders on Earth, and that their bites are harmless because their fangs cannot penetrate skin. This claim is false. In reality, the term ‘daddy longlegs’ is not scientific and refers to three distinct groups, only one of which is a true spider.
The genuine spiders labeled as daddy longlegs belong to the family Pholcidae, commonly called cellar spiders. The nickname is also applied to crane flies (family Tipulidae), insects with very long legs that are frequently confused with both pholcid spiders and mosquitoes. Some refer to them as mosquito hawks, adding to the confusion.
Crane flies can be identified when they spread their wings, but the third group sharing the nickname is even more misleading. These wingless arachnids belong to the order Opiliones, commonly known as harvestmen. Unlike spiders, harvestmen have a single fused body segment, two eyes, and lack venom glands. Consequently, two of the three organisms referred to as daddy longlegs are non‑venomous. The remaining group—the cellar spiders—does possess venom, but its potency and relevance to humans differ.
Within the family Pholcidae—commonly referred to as cellar spiders—there are almost 2,000 species, all noted for their exceptionally long legs. These appendages allow the spiders to propel silk in a ballistic manner to ensnare prey larger than themselves, keeping the spider’s body safe. Additionally, the long legs facilitate rapid locomotion across varied surfaces and help detect vibrations that signal approaching prey.
Like most spiders, pholcid species are venomous, but their toxins are adapted to subdue insects such as flies and bees. The venom is insufficient to cause harm to humans. Moreover, the chelicerae of these spiders lack the strength to puncture human skin—an aspect of the myth that holds some truth. A 2019 study in Frontiers in Ecology and Evolution compared the venom of Physocyclus mexicanus to that of the western black widow (Latrodectus hesperus) in mice; the black widow’s venom proved more potent, underscoring that pholcid venom is comparatively mild.
Australia hosts some of the world’s most potent venomous spiders, notably the funnel‑web species of the family Atracidae. These spiders construct funnel‑shaped webs that trap prey. The Sydney funnel‑web (Atrax robustus) is especially infamous, having caused 13 fatalities before antivenom was introduced in 1981. While no deaths have been recorded since, the species continues to bite 30–40 people annually.
Given the lethal history and formidable look of funnel‑web spiders, it is surprising that the slender daddy longlegs gained notoriety for supposed danger. A likely source of confusion is the brown recluse spider (Loxosceles spp.), which, while not the world’s most venomous, is among the most dangerous in the United States and rivals black widows in potency. Brown recluses share a long‑legged appearance with pholcids, but can be distinguished by body size and other distinguishing features. They are widespread across the U.S. and typically bite only when provoked.
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