Halloween blog: spider science
With Halloween almost upon us we thought we should give you a scare of the eight-legged variety.
So I asked George McGavin, of the Oxford University Museum of Natural History, about scary spider encounters and why arachnids deserve gasps of wonder along with our yelps of fear...
OxSciBlog: What has been your favourite encounter with a spider?
George McGavin: My favourite encounter has got to be when I found the goliath bird-eating tarantula (Theraphosa blondi) when filming Lost Land of the Jaguar in Guyana. We went out after dark to scour the forest close to base camp - after several hours we had not found anything and I was beginning to think that we'd never find one when Bruds, one of the rangers, radioed to say he had found a likely burrow.
Sure enough the burrow was occupied by a large female which I was able to coax out using a blade of grass as a lure. Once in the open I blocked the hole with my machete. The spider was the size of a soup plate and although equipped with half inch long fangs, their main defence is to flick tiny harpoon-like hairs in the face of any attacker. This she did with great enthusiasm and the air was soon filled with her abdominal hairs. They got in my face, eyes and throat but I was not going to be deterred.
When she had calmed down I gently picked her up to show to the camera. She was a real star and even leapt off my hand towards the cameraman - a great performance!
OSB: In evolutionary terms how successful are spiders?
GMcG: Arachnids appeared on Earth around 420 million years ago. Today there are about 80,000 species worldwide. They are a very old group and include things like mites, ticks, scorpions, whip-spiders, harvestmen and pseudoscorpions. The true spiders have mastered the use of silk for prey capture, transport, protection and other uses.
OSB: How important are spiders to preserving ecosystems?
GMcG: As terrestrial carnivores arachnids they have a huge impact on populations of insects and other small invertebrates. A hectare of grassland may be home to several million spiders and other arachnids. One species lives in water in a specially constructed silk diving bell and can prey on small fish fry. Recently the first herbivorous spider has been discovered.
OSB: Why do you think many people have a fear of spiders?
GMcG: In the UK 7 million people are arachnophobic to some degree. While it is true that there are a dozen or so species of spiders whose fangs are strong enough to break human skin they will not do you any harm and allergic reactions to spider bites are very rare.
In Australia, however, where there are several dangerous species, people seem a bit more relaxed about their eight-legged friends. In the middle ages in Europe spiders were associated with diseases and death and I wonder if this might be might origin of our phobia.
OSB: What do scientists still need to find out about spiders?
GMcG: While the arachnids are not as diverse as the insects there are still many more species waiting to be discovered. We actually know very little about the lives of most spider species.
Dr George McGavin is an Honorary Research Associate at the Oxford University Museum of Natural History.