Coming off a weekend in which I collected 30-plus mosquito bites while my girlfriend received four, I have a few mosquito-related questions: What attracts mosquitoes to people? Do we smell delicious to them? Do I smell particularly more delicious than my girlfriend?
Here's hoping the little bastards die a slow, painful death this year.
Itchy As Hell
On many camping trips in his Midwestern youth, young Science spent much time pondering these same questions—mostly while itching and scratching. While DEET-based repellents work (at least somewhat), it would be so much more satisfying to know how the bastards find us, and possibly use this knowledge to block their attacks. Now, thanks to some clever work by Doctors Syed and Leal at UC Davis, we have some answers.
Mosquitoes, it's long been hypothesized, smell us out—following a trail of scent to their next meal. One obvious candidate is our breath—specifically, the carbon dioxide we release as we respire. Studies of mosquitoes have shown the drawing power of carbon dioxide (spawning a whole series of CO2-spewing mosquito defenders in SkyMall catalogs), as well as a few other possible odorants produced by humans.
The authors of the study noted that the Culex mosquito species common in North America delight in dining on humans and birds. Whatever factors mosquitoes are using to find their prey, at least a few key ones are shared between human and birds. Next step? Collect odorants from humans and birds, with a contraption involving tape, pipettes, absorbent mesh cloth, and aluminum foil (the birds were harder to recruit than the humans). Humans of a variety of races and ethnicities were sampled, with four odorants clearly shared among all humans. One of these odorants—a deceptively small and simple chemical molecule called nonanal—was found to be shared between human and bird. Intriguingly, this nine-carbon aldehyde has a delightful fruity and beguiling odor.
Next, using the smell-sensing antennas themselves, it was confirmed that our mosquitoes could sense this chemical, reacting vigorously when samples were applied. Traps laced with nonanal attracted more mosquitoes as compared to controls. Still, traps laced with carbon dioxide attracted approximately 40 times more mosquitoes than those with nonanal alone. The combination of nonanal and CO2 was the real blockbuster; together, carbon dioxide and nonanal showed synergy—attracting mosquitoes with a real potency.
Science speculates that you might produce more nonanal (or some other attractive odor) than your friend, explaining your excess bites. You, potentially, are sweeter smelling to mosquito and human. On the other hand, mosquito spit and your immune system collaborate to make mosquito bites; perhaps you were dined on the same amount as your girlfriend and just reacted more strongly.
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