Vampire spiders and “human” scent

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There is a recent study out about how vampire spiders are attracted to human scent. These spiders eat mosquitoes, and in Africa where they live, those mosquitoes often have recently feasted on human blood.

Jumping or Vampire Spider

As noted in this article, “Jumping spiders that love smelly socks could help fight malaria“, the spiders are often found in tall grass adjacent to human dwellings. What the study found was that the spiders spend more time (i.e., are more attracted to) smelly socks, and the conclusion is that they are thereby more attracted to a human odor. You can also see more in this blog post, Vampire spider drawn to the smell of human feet.

So, what is wrong with this picture?????

Who says that smelly socks smell like humans? Smelly socks have their odor because of all the bacteria that live inside shoes, where they thrive on the warm, dark, moist environment there. Real bare feet are not “smelly.” Yes, they probably have a (faint) odor, but it is a real stretch to say that the smell of the bacteria have anything to do with bare feet, or the odor of humans. If anything, the feet of those who regularly go barefoot probably smell more of what they are walking in.

And this study was in Kenya, where many people there really do go barefoot (or at least sandaled) all the time. The whole study is biased by a shod viewpoint. How would these spiders become familiar with the odor of shod feet in Kenya?

Yet, we are assured, in this comment, that “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.” It may be that really sweaty socks are used as an attractant, but, really, how do they know that those arthropods are not somehow attracted to some other aspect of the bacteria growing on those socks, and not some human odor? (I also note that synthetic materials are not as conducive to bacterial growth!). How do we know that these mosquitoes and spiders are not tagging on the bacteria themselves? I somehow doubt that such a test had been done, and that these shoddy researchers have just assumed that this is a valid indicator.

It is always valuable to look beneath the unexamined assumptions of various studies.

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2 Responses to “Vampire spiders and “human” scent”

  1. Dan Says:

    I’ve heard that mosquitoes are attracted to sweat. There’s lots of sweat in socks that have been stuck in smelly, bacteria-laden shoes all day, all week, etc. I don’t think the mosquitoes are interested in the bacteria in there, but I’m not a scientist so I can’t say for sure.

    I go barefoot as much as possible, yet mosquitoes still find my bare toes and soles to be desirable feasting grounds in the summer. I would think bare feet must sweat to some degree in humid temperatures, but obviously not nearly to the level they do when shod.

    But I will not cover up my bare feet to avoid mosquito bites; I spray them with bug spray and hope for the best!

  2. Bob Neinast Says:

    There is an interesting web page here, “What attracts mosquitoes?”. High on the list: carbon dioxide, from our exhalations. At the very end: “One of the studies by entomologist Daniel L. Kline showed that worn human socks alone attracted very few mosquitoes. However, a significant increase occurred to CO2-baited traps when combined with a worn sock for most mosquitoes, including species of Aedes, Anopheles, Coquillettidia, Culex, Culiseta, and Psorophora.”

    I’m not convinced that the attraction by mosquitoes has anything to do with “human scent”, and I suspect they’ve never done the carefully controlled studies to show that it is.

    If anybody can point me to a study to show that I am wrong, I’d love to see it (and will admit my error).

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