In Kenya, a vampire spider is hunting down its prey by tracking the smell of human feet. If that sounds nightmarish, don’t panic – the spider Evarcha culicivora is only an indirect vampire. It’s not interested in attacking humans; it’s after mosquitoes that have fed on mammal blood. If anything, the spider is our ally – it kills female Anopheles mosquitoes that spread malaria.
Robert Jackson from the University of Canterbury discovered the spider in 2003. He quickly showed that it likes to target malarial mosquitoes, especially those that had just fed on blood, and it can recognise them based on either appearance or smell. And in 2009, Jackson, together with his colleague Fiona Cross, showed that the blood is both an aphrodisiac and a meal for the spiders. When they’ve drunk their fill, they become more irresistible to the opposite sex.
Now, Cross and Jackson are back with a new study, which shows that Evarcha likes to hang around humans. After all, what better place to find a blood-filled mosquito than the source of the blood?
The duo wafted the scent of human socks into test tubes occupied by captive spiders, which could leave at any time. They were more likely to stay if the smell came from a sock that a human volunteer had worn for 12 hours beforehand. The scent of unworn sock was less attractive. They spent anywhere from 15 to 30 minutes longer sampling the fragrance of feet, and spiders both male and female, young and old, behaved in the same way.
Evarcha’s keen sense of smell is unusual for a jumping spider, a group that’s better known for their exceptional eyesight. It’s possible that its sense has evolved to mirror that of its prey. Both the mosquitoes and the spiders are drawn to the smell of humans, in search of mouthfuls of blood. The only difference is that the mosquito takes it from our bodies and the spider takes it from the mosquito.
Reference: Cross & Jackson. 2011. Olfaction-based anthropophily in a mosquito-specialist predator. Biology Letters http://dx.doi.org/10.1098/rsbl.2010.1233
A gallery of incredible spiders
February 15th, 2011 at 7:24 pm
awesome post, love the spider stories.
February 15th, 2011 at 9:53 pm
Love the spider stories, but the pictures…not so much. Oh well, got to get over my heebie-jeebies some day.
February 16th, 2011 at 4:17 am
Are these spiders then a vector for spreading malaria? Such as, if a spider eats a malaria-infected mosquito, walks around for a while and eventually dies, will a new mosquito come and suck the spider’s blood and get infected with malaria?
February 16th, 2011 at 4:39 am
@ Marco: Waiting for someome more qualified than me to reply, I’m gonna say: no, the spider is not a vector. I don’t think mosquitos would suck blood from dead spiders
February 16th, 2011 at 6:18 am
Dear Ed: I love you.
February 16th, 2011 at 8:27 am
What an interesting article! Thankfully they don’t bite humans, they’re so cute!
February 16th, 2011 at 11:27 am
@Marco A. The spiders are not a vector for the spread of disease. Almost all mosquitoes are very specialized and will only go after certain types of animals that fit their feeding needs. Spiders blood is different from mammal blood and would be incompatible to the mosquitoes.
Kind of neat article.
February 16th, 2011 at 12:59 pm
The title of this story is hilarious. Great post Ed.
February 17th, 2011 at 9:31 am
I just have to point out that they are not being drawn to the smell of human feet. As the study says, they are drawn to the smell of dirty socks, which is composed almost entirely of the smell from the various bacteria that reside inside the warm, damp environment inside shoes. But I don’t see how it could be said that this smell could be called a human smell.
Feet that are continuously bare tend not to smell much, or smell like what they have been walking on. But they would certainly have a different set of bacteria because of the different environmental conditions.
Since this is Kenya, a lot of the people there still go barefooted or sandaled, so it is not clear to me why these spiders are attracted to this particular smell, but it seems a real stretch to relate it to mosquitos and malaria.
February 17th, 2011 at 1:48 pm
Ahcuah:
Real sweaty socks (as opposed to synthetic, which just don’t work as well) are a commonly-used attractant for human-feeding mosquitoes, so it works well enough as a “human” smell for some of our ectoparasites. I’m not sure if anyone’s compared the microbiome of frequently-socked feet to frequently-sockless feet, but I think it’s reasonable of the researchers to stick with an known attractant from the mosquito literature when dealing with mosquito predators, especially since the important volatile components are still being worked out. Fixing that serious gap (an active area of research for the purposes of synthesizing mosquito attractants for traps) seems a little beyond their scope.
February 18th, 2011 at 2:04 am
Makes me wonder if the spiders could be used as malarial vector controls. I’ve thought the same thing about bat houses.
February 19th, 2011 at 12:24 am
Yeah, one catch I find with this is… the mosquitos have to bite you first.
February 19th, 2011 at 6:49 pm
I might have to do this kind of research. I m zealous . Awesome post. So many wonderful things in the nature to help the human kinds.