Tuesday, 3 October 2006

Keeping in Pholcus

The story goes like this: the daddy long legs is the most venomous spider in the world but it can't hurt us because its fangs are too small to puncture human skin. Just as well, too. Pholcids are everywhere—in those dusty lace webs in the corners of the bathroom, garage, shed, verandah ...

But is the story true? Are they thwarted killers? No. Not when it comes to humans, anyway.

The Mythbusters had a go at this tall tale. First, they measured the length of the fangs, which turned out to be plenty long enough to penetrate human skin. Then Adam Savage shoved his arm in a cage of spiders. They bit him repeatedly, but the worst response was a mild local reaction.

The Mythbusters' conclusion? Busted!

How did such an inoffensive creature get lumbered with this reputation? Well, pholcids may be harmless to us but they aren't quite as harmless to other spiders. They prey on any individual they can subdue. And that's where the story's nucleus almost certainly lies.

Because they live in houses and other domestic areas, pholcids tend to encounter those other spiders that associate with humans, including the black house spider (Badumna) and the infamous red back (Latrodectus). The former has been implicated in serious bites. And we all know about the red backs. (For non-Australians, think black widows.)

Here's the logic: if a daddy long legs can kill those nasty species then it must be mega-nasty itself.

But it doesn't work like that. The pholcid's long legs allow it to wrap prey in silk, while keeping out of range of the victim's fangs. It can then find a vulnerable spot to inject its venom, which works at a slow pace. There's no super-venom that kills in moments. So unless you're another spider, daddy-long-legs are harmless.

No comments: