Urban legends have a way of spreading and persisting long after science disproves them. Most Americans have heard and probably believe that daddy-longlegs are the most poisonous spiders in the world, but that their fangs are too small to penetrate human skin. This is a myth. There has never been any science to back up this claim, and recent investigation has actually disproven it.
One huge issue with this myth is that there are multiple organisms that are referred to as daddy-longlegs—only one of which is actually a spider in the Order Araneae.5 There are two other groups that go by the same common name. One of the other types of daddy-longlegs is in the Order Opiliones, and they are otherwise known as harvestmen or opilionids. These organisms have only one basic body segment (spiders have two), have a maximum of two eyes (spiders have 8), cannot produce silk for webs, and do not have venom glands or fangs.5 This being the case, they cannot even produce venom, let alone have the most deadly venom on Earth. The other non-spider daddy-longlegs is common in the U.K. and is also called the Crane fly. It is an insect and, like harvestmen, is not a spider, nor is it venomous.1
As for the daddy-longlegs spider—which is also known as the Pholcid house spider found in Australia4—the myth has never been proven with science.3 The television show MythBusters set out to test the validity of this myth in a 2004 episode. They reported that the spider’s fangs were able to penetrate the skin of a man’s arm. The bite resulted in a brief and mildly uncomfortable burning sensation. This disproved one half of the myth. They also compared the venom of the daddy-longlegs spider to the venom of a Black widow spider and discovered that the Black widow’s venom was more potent, thus debunking the second half of the myth.2 If MythBusters doesn’t meet your credibility standards, other studies have been performed in labs such as the University of California, Riverside, yielding similar results.5
Some speculate that this myth probably originated from observations of daddy-longlegs spiders killing and eating the much larger redback spiders3, but studies like the ones mentioned above show that the venom is not that potent—even for insects.
1) Crane fly | insect. (2014, December 23). Retrieved June 25, 2015, from http://www.britannica.com/animal/crane-fly
2) Episode 13: Buried in Concrete, Daddy Long-legs, Jet Taxi. (2004, February 15). Retrieved June 25, 2015, from http://mythbustersresults.com/episode13
3) Gray, M. (2014, January 30). Daddy-long-legs Spider, Pholcus phalangioides – Australian Museum. Retrieved June 25, 2015, from http://australianmuseum.net.au/daddy-long-legs-spider
4) The Spider Myths Site. (2010, September 1). Retrieved June 25, 2015, from http://www.burkemuseum.org/spidermyth/myths/daddyvenom.html
5) UCR Spiders Site. (n.d.). Retrieved June 25, 2015, from http://spiders.ucr.edu/daddylonglegs.html