No. The daddy long-legs spider is venomous, but not dangerously venomous to humans, and it is certainly not the most venomous spider in the world. The other half of the famous story is wrong too: its fangs are small, but they can pierce human skin, and if one ever bit you, the reaction would be minor and short-lived.
So how did a harmless-looking house spider end up with a reputation for the deadliest venom of all? The answer involves a redback, a very effective hunting technique and a great deal of repetition.
Three animals, one nickname
Part of the confusion is that “daddy long-legs” is a nickname for several completely different animals. In Australia, when someone points to the spindly spider hanging in the corner of a ceiling, garage or shed, they almost always mean Pholcus phalangioides, also called the cellar spider. It is a genuine spider in the family Pholcidae, with eight legs, a two-part body and venom glands, and Museums Victoria records it across mainland Australia and Tasmania, indoors and in sheltered spots outside.
| Nickname used for | What it actually is | Venom? |
|---|---|---|
| Daddy long-legs spider (Pholcus phalangioides) | A true spider, the one in Australian ceilings and sheds | Yes, but not medically significant to people |
| Harvestman (order Opiliones) | An arachnid, but not a spider; one body section | No venom glands or fangs |
| Crane fly (in some countries) | An insect with six legs and wings | None |
The myth gets told about all three, but only the spider has venom at all, so that is the one this article is about.
Venomous, not poisonous
Most people ask whether daddy long-legs are poisonous, but technically venomous is the right word. A venomous animal delivers toxins through a bite, sting or other specialised structure, while a poisonous animal is harmful when its toxins are eaten, absorbed or touched. The daddy long-legs uses venom to subdue its prey, so it is venomous. That does not make its venom dangerous to people. Museums Victoria’s spider myths article points out that researchers who analysed it concluded its effects on humans and other mammals are inconsequential, and the museum’s species page rates it as harmless, with at most a local reaction such as redness, swelling, burning or itching.
How a redback started the rumour
Nobody can point to the moment the myth was born, but there is a very likely culprit: the daddy long-legs’ choice of dinner. It kills and eats other spiders, including redbacks, and the Australian Museum says the myth probably grew from people seeing exactly that. It sounds impressive until you look at how it does it. A daddy long-legs does not overpower a redback in a close fight. It uses its exceptionally long legs to throw silk over the other spider and wrap it up from a relatively safe distance, then moves in to bite once the prey can no longer fight back. Its success against redbacks says a lot about its hunting skill, and very little about the strength of its venom.
There is a second reason the logic does not hold. Venom does not work the same way on every animal. A toxin that is very effective against a spider or insect will not necessarily have any meaningful effect on a mammal, because different animals have different physiology and nervous systems. So killing one of Australia’s venomous spiders does not mean the daddy long-legs must be even more dangerous to people. The hunting method matters just as much as the venom.
Yes, it can bite you (but it won’t do much)
The other half of the legend, that its fangs are too small to pierce human skin, is also wrong. The Australian Museum notes that the fangs are only about 0.25 millimetres long, but a test on the US television show MythBusters showed they can pierce human skin, and the stinging sensation it produced was very short-lived. Wikipedia’s summary of the episode adds that the presenters were also told about an experiment in which mice injected with daddy long-legs venom reacted far less than mice injected with black widow venom.
That does not mean you should expect to be bitten. Daddy long-legs spiders are reluctant to bite people, and when disturbed they are far more likely to run away or start vibrating rapidly in their web; the Australian Museum describes the spider becoming a blur to anyone watching. If one did bite, you might feel a brief sting, perhaps with a little local redness or itching, and that would be the end of it.
The Aussie spiders that do deserve respect
Australia’s genuinely dangerous spiders probably help the myth survive. A story about a harmless-looking spider secretly carrying the world’s deadliest venom sounds a lot more believable when you share the country with funnel-webs and redbacks. If you want a spider that deserves serious respect, the male Sydney funnel-web (Atrax robustus) is the one. The Australian Museum says it has one of the most toxic venoms, to humans, of any spider, while females and juveniles are much less toxic. The Australian Reptile Park, which milks funnel-webs to produce the antivenom, reports 13 recorded deaths before the antivenom arrived in 1981, and none since.
Redbacks are far more common in backyards, and their bites can cause significant pain, sweating and other symptoms, but they are not life-threatening. According to Healthdirect, most redback bites can be treated at home, and the NSW Poisons Information Centre notes that routine use of redback antivenom is no longer recommended, after trials found it worked little better than a placebo. Funnel-webs are a different matter: Healthdirect says that if you think you have been bitten by a funnel-web or any big black spider, you should call triple zero (000), keep still and use a pressure immobilisation bandage while waiting for help. Do not use that bandage for a redback bite. Compared with any of that, a daddy long-legs in the laundry is not worth a second thought.
Should you kill a daddy long-legs?
There is certainly no need to because of its mythical venom. But there is a twist. As Australian Geographic explains, Pholcus phalangioides is not native. It originally comes from subtropical Asia and spread around the world with people, becoming one of the most common spiders in Australia. It does a useful job keeping other spiders, including redbacks, away from your house, but the spiders it affects most are usually our native species. So it is not a dangerous intruder, and not an essential part of the local ecosystem either. If you leave it alone, it will quietly get on with hunting in its corner.
Its reputation, in other words, is far more dangerous than the spider itself. The legend gets both halves wrong: the venom is not deadly to us, and the fangs are not too small to bite. What it does have is reach, silk and patience, which turn out to be all it needs to take on a redback. It is a good reminder that the most repeated animal “facts” are often the least checked, as I also found looking into whether sharks get cancer. And if you like animals with unexpected hunting tricks, those that hunt by sound are just as surprising, as my post on echolocation shows.
If you are bitten by a spider and are unsure what it was, call the Poisons Information Centre on 13 11 26 for advice, or 000 in an emergency.
Sources
- Australian Museum: Daddy-long-legs Spider
- Museums Victoria: Pholcus phalangioides, Daddy Long-legs
- Museums Victoria: Top spider myths
- Australian Geographic: Fact file, daddy-long-legs spider
- Wikipedia: Pholcidae (including the MythBusters test)
- Australian Museum: Sydney funnel-web spider
- Australian Reptile Park: Spider venom program
- Healthdirect: Spider bites