Smelly feet prove irresistible to malaria mosquito predator

University of Canterbury researchers Dr Fiona Cross and Professor Robert Jackson have found that the East African spider that feeds on a notorious malaria-carrying mosquito is attracted to smelly human feet.

Dr Cross, whose research is supported by a three-year Foundation for Research, Science and Technology Postdoctoral Fellowship and Professor Jackson are currently in the Lake Victoria region of East Africa studying a spider, Evarcha culicivora in its native habitat. The same area is also the habitat for many mosquitoes, including the An. gambiae which Dr Cross describes as "notorious for being exceedingly effective as a vector of human malaria."

"Evarcha culicivora is the only known predator that specifically targets blood-carrying mosquitoes as its preferred prey. What is more, its preferred mosquitoes are from the genus Anopheles, which are vectors of malaria."

Dr Cross' findings have just been published in the prestigious Royal Society journal Biology Letters and may eventually have a part to play a part in the ongoing challenge of finding the means to control human malaria.

In the meantime Dr Cross is excited by what her findings may mean.

"It really is quite unprecedented that a spider should find human odour attractive. One of the reasons why An. gambiae is so effective as a human-malaria vector is that it is anthropophilic i.e. it is attracted to humans. Part of what 'anthropophily' means in this instance is that this mosquito species is attracted to human odour.

"E. culicivora lives especially in and around people's houses in East Africa, and An. gambiae is particularly often its prey. It is rather extraordinary that An. gambiae and its predator, E. culicivora, both find human odour to be attractive. This suggests a remarkable convergence."

Dr Cross's and Professor Robert Jackson’s previous research had determined that E. culicivora used olfactory search images when looking for its next meal or mate but their current field trip has enabled them to carry out further experimental research.

"We had a suspicion that human odour is attractive to E. culicivora before we even ran the experiment. We generally find these spiders in the tall grass next to houses or other buildings occupied by people.

"We are currently based next to Lake Victoria in Eastern Kenya, and we often notice these spiders venture into our houses. Even when we have used these spiders in other experiments, they seemed to act a lot calmer around us than other species of jumping spider that we've tested.

"Knowing that E. culicivora's prey finds human odour so attractive, we decided we should see if E. culicivora also finds human odour attractive. It wasn't particularly hard, since using smelly socks is a quick and convenient way of testing for attraction to human odour."

Dr Cross is now keen to pursue the implications raised by her research.

"It might creep some people out to know that there is a spider in this world that actually loves us, but a finding like this has some interesting implications. There are so many ways in which scientists around the world are currently trying to combat malaria. Often it seems like people want and expect a magic bullet that will eradicate this disease. We hesitate to say anything is impossible, but a magic bullet in the foreseeable future seems unlikely with a disease as complex as malaria.

"Evarcha culicivora will never be the magic bullet for malaria, but it might be a small piece in the malaria puzzle. And it's something that's there in the environment for free. Why not do what we can to find out about this remarkable predator?"

ENDS

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