VENOMOUS SPIDERS

White-tailed spiders and 

Daddy Long Legs: An urban myth

Today I spent most of the day at a First Aid course as well as a couple of hours driving a school bus, so not many new posts on the blog today. Sorry about that, readers.

A Daddy Long Legs spider

During discussions at the First Aid course the subjects of poisons came up and in particular the Australian White-tailed spider which can give a nasty bite. For many years it has been claimed that the White-tailed spider is venomous because it eats Daddy Long Leg spiders and the Daddy Long Legs is actually the world’s most venomous spider, but with fangs not powerful enough to penetrate human skin. This claim was also mentioned today.

When I suggested that the connection between the White-tail and the Daddy Long Legs may just another urban myth, the tutor replied that it was a definite known fact that the White-tail is only venomous because it eats the world’s most venomous spider, the Daddy Long Legs.

So when I got home I went on the internet and did the research. Here is part of what I found.

White-tailed spider

From Wikipedia, the free encyclopedia

White-tailed spiders are medium-sized spiders native to southern and eastern Australia, and so named because of the whitish tips at the end of their abdomens. Common species are Lampona cylindrata and Lampona murina. Both these species have been introduced to New Zealand.^[1]

A White-tailed spider

White-tailed spiders are vagrant hunters who seek out prey rather than spinning a web to capture it. Their preferred prey is other spiders and they are equipped with venom for hunting.
They are known to bite humans and effects may include local pain, a red mark, local swelling and itchiness; rarely nausea, vomiting, malaise or headache may occur. Ulcers and necrosis have been attributed to the bites, but a scientific study by Isbister and Gray (2003) showed these were probably caused by something else, as the study of 130 white-tailed spider bites found no necrotic ulcers or confirmed infections.^[2]

AND from the Straight Dope Science Advisory Board

Is a Daddy Long Legs the most poisonous spider?

Possible envenomation

Is there any truth to this oft-repeated tale?

Daddy-longlegs (Opiliones) - these arachnids make their living by eating decomposing vegetative and animal matter although are opportunist predators if they can get away with it. They do not have venom glands, fangs or any other mechanism for chemically subduing their food. Therefore, they do not have poison and, by the powers of logic, cannot be poisonous from venom. Some have defensive secretions that might be poisonous to small animals if ingested. So, for these daddy-long-legs, the tale is clearly false.
Continued below . . . . .

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HAPPY READING

Daddy-longlegs spiders (Pholcidae) - Here, the myth is incorrect at least in making claims that have no basis in known facts. There is no reference to any pholcid spider biting a human and causing any detrimental reaction. If these spiders were indeed deadly poisonous but couldn't bite humans, then the only way we would know that they are poisonous is by milking them and injecting the venom into humans. For a variety of reasons including Amnesty International and a humanitarian code of ethics, this research has never been done. Furthermore, there are no toxicological studies testing the lethality of pholcid venom on any mammalian system (this is usually done with mice). Therefore, no information is available on the likely toxic effects of their venom in humans, so the part of the myth about their being especially poisonous is just that: a myth. There is no scientific basis for the supposition that they are deadly poisonous and there is no reason to assume that it is true.

What about their fangs being too short to penetrate human skin? Pholcids do indeed have short fangs, which in arachnological terms is called "uncate" because they have a secondary tooth which meets the fang like the way the two grabbing parts of a pair of tongs come together. Brown recluse spiders similarly have uncate fang structure and they obviously are able to bite humans. There may be a difference in the musculature that houses the fang such that recluses have stronger muscles for penetration because they are hunting spiders needing to subdue prey whereas pholcid spiders are able to wrap their prey and don't need as strong a musculature. So, again, the myth states as fact something about which there is no scientific basis.

In summary

For true daddy-long-legs, the opilionids, the myth is certainly false, and for the daddy-long-legs spiders it is certainly not based on known facts.

And then from Burkemuseum.org

Myth: The daddy-longlegs has the world's most powerful venom, but fortunately its jaws (fangs) are so small that it can't bite you.
Fact: That is a full-fledged Urban Legend, with no basis in fact whatever. This legend is so widespread that many people believe it who should really know better, including some teachers and TV documentary producers.

Three different unrelated groups are called "daddy-longlegs." Harvestmen (below left) have no venom of any kind. None at all! Same with crane flies (below right). Pholcid spiders (below center) have venom (like almost all spiders) but there's nothing special about it; in fact, a recent study showed that pholcid venom is unusually weak in its effect on insects. This myth is debunked at greater length on Rick Vetter's web site.

So getting rid of Daddy Long Legs spiders from your house is not the way to get rid of the White-tails. It would be better to use a recommended insect repellent in all the dark corners of the house including inside the roof.