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| Not the most appealing-looking house guest, but it could help combat malaria |
By Victoria Gill
Science and nature reporter, BBC News
A spider that preys on the malaria-carrying mosquito Anopheles gambiae is attracted to the odour of sweaty socks, according to a study.
The jumping spider appears to have evolved an affinity for smelly human feet in order to help find its prey.
The team reports its findings in the journal Biology Letters.
They say that people might be able to "recruit" this East African jumping spider, Evarcha culicivora, in the battle against malaria by encouraging the arachnids to live in their homes.
Smelly experiment
Fiona Cross, from the University of Canterbury, and Robert Jackson, from the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya, carried out the study.
They were interested in this species because it is the only known predator that specifically preys on blood-carrying mosquitoes.
"We had a suspicion that human odour was attractive to the spiders before we even ran the experiment," Ms Cross told BBC News. "We generally find these spiders in the tall grass next to houses or other buildings occupied by people."
To test this suspicion, the team devised an aroma-based experimental set-up called an olfactometer.
They put each "test spider" into a small holding chamber into which air was pumped, either from a box containing a clean sock or one containing a worn (and therefore smelly) sock.
Each spider was able leave its holding chamber at any time and escape into an exit chamber, which did not have sock-scented air pumped into it.
The spiders supplied with the aroma of worn socks always remained in the holding chamber for longer than those exposed to the freshly washed sock.
Ms Cross said it was "unprecedented that a spider should find human odour attractive".
But, she added, the discovery tied in with some of the spiders' remarkable behaviour.
"When they smell blood, they can launch into feeding frenzies where they kill up to 20 mosquitoes in rapid succession, and not necessarily to eat all of them," she explained.
"We need to learn more about why they do this - they really do go quite crazy when they are in the vicinity of blood."
Anti-malaria arachnid
It may be a rather ugly, bloodthirsty little creature, but Evarcha culicivora could help in the ongoing and complex battle against malaria.
"It's something that's there in the environment for free," said Ms Cross. "So why not do what we can to find out about this remarkable predator?"
She and her colleagues are currently trying to find out what exactly people might be able to do to attract the spiders into their homes, without also attracting the mosquitoes.
The scientists say that, in malaria zones, people should welcome these particular creepy crawlies into their houses.
http://news.bbc.co.uk/earth/hi/earth_news/newsid_9398000/9398408.stm
(Submitted by Dawn Holloway)
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