Blood enlarged female mosquito. Photograph by James Gathany, CCD Public Health Image Library.
This week, I set off to find out once and for all if and why mosquitoes are attracted to some people more than others.
The good news is, I’m not crazy! Mosquitoes do seem to be attracted to some people more than others for various reasons. Unfortunately, the question of why can’t exactly be answered once and for all — at least with the information that is currently available. That isn’t to say though that scientists don’t have a good idea about what attracts mosquitoes to people and, perhaps more importantly, what repels them.
Difficulties in Generalized Answers
It’s so hard to create generalizations about causes of attraction because of the differences among mosquito species that exist. Humans bodies also give off a lot of trackable information too (heat, movement, chemical compounds in body odor, etc.), making it that much more difficult to pinpoint a specific reason.
There are over 3,000 species of mosquitoes worldwide, and many species behave differently from each other in terms of aggressiveness, preferred prey, and the chemicals that they are more attracted to. For example, in a study from the Imperial College London (check it out here), scientists found that different baits were more attractive to different species. The baits used were carbon dioxide and human body odor — both known attractants of mosquitoes. They observed that all species tested were more attracted to both traps as bait concentrations increased, but that there was a difference in which of the baits attracted a larger portion of the mosquitoes across different species. This shows that although the generalization that mosquitoes are attracted to carbon dioxide and chemicals in human body odor can be made, this generalization doesn’t show how the strongest factor of attraction can be different for different species.
Mosquitoes also take into account many different factors when seeking blood, as Dr. Leslie Vosshall explains in an interview with The Daily Beast. First, the mosquito detects the smell of body odor and carbon dioxide (mosquitoes can detect carbon dioxide from 30-40 feet away). Then, as the mosquito moves closer, it is able to detect heat and movement. Finally, when the mosquito lands, it notices taste. Dr. Vosshall notes that in her own experience, mosquitoes will fly towards her and land on her, but then fly off without biting, highlighting the fact that taste can play a roll in mosquito attraction.
What We Know
Although the complexity of the issue keeps us from a black or white type of answer, scientists do agree that certain things attract mosquitoes in general. For example, carbon dioxide (released from skin and by exhaling) and lactic acid (a chemical compound in skin that is especially present when exercising) have been shown to attract mosquitoes, as seen in the Imperial College study mentioned before.
However, these attractors don’t explain why some people get bitten more than others; we all emit CO2 and have lactic acid. Also, as Dr. Vosshall mentioned, it is only known that body odor and carbon dioxide are very important in a mosquito’s initial attraction.
Mosquitoes avoiding DEET (a mosquito repellent) treated hand on right. Photograph by Greg Allen, USDA-ARS.
Instead of focusing on analyzing what about a person makes them more attractive, researchers have begun to explore the possibility that some people emit extra, repellent chemicals that either mask or actively repel mosquitoes. Researchers at Rothamsted Research in the U.K. have collected and analyzed the body odors of known mosquito-attracting individuals and mosquito-resistant individuals and identified certain chemical compounds that were present in the resistant group but not the attractive group. Many of these chemicals are believed to be related to stress, but it is still not known if stress leads to less mosquito bites. You can read more about Rothamsted Research’s work here and here.
The answer to my question wasn’t as neat and specific as something like “eating bananas attracts mosquitoes” or “taking vitamin B-12 repels them” (both are just wives tales), but then again, nature wouldn’t be as exciting and beautiful as it is if all of the answers were that simple.
Other Cool Mosquito-Related Links
- Active ingredients to search for when buying mosquito repellent: http://www.cdc.gov/westnile/faq/repellent.html
- Slow motion mosquito DEATH BY LASER BEAM (yay science!): http://www.youtube.com/watch?v=BKm8FolQ7jw
- What happens inside you when a mosquito bites: http://www.dailymail.co.uk/sciencetech/article-2385937/What-REALLY-happens-mosquito-bites-Scientists-capture-parasite-bites-sucks-blood-gruesome-video.html