How do mosquitoes find food? First, they smell you, scientists say

New research shows that mosquitoes find targets by following the scent of the air we exhale, then using sight and body heat sensors to close in.

Pat Wellenbach/AP/File
A Cattail mosquito is held up for inspection at the Maine Medical Center Research Institute in South Portland, Maine, Sept. 8, 2010. New research shows that mosquitoes identify targets based first on the scent of carbon dioxide, then on visual and temperature cues.

To investigate how mosquitoes home in on their targets, biologists from the University of Washington and the California Institute of Technology tracked them tracking us.

The researchers found that mosquitoes rely on a variety of senses to find their meals in a process they divided into stages: first they pick up a scent, then they follow a visual cue, and once they are close enough to the target they sense its body heat.

The scent that alerts mosquitoes to the proximity of a potential target is not that of blood, but of carbon dioxide, the gas we exhale. Mosquitoes can smell the gas from as far as 30 feet away, University of Washington researcher and co-author on the paper Jeff Riffell explained in a news release.

“Carbon dioxide is the best signal for a warm-blooded animal, and they can sense that from up to 30 feet away – quite a distance,” Mr. Riffell said. “And then they start using vision and other body odors to discriminate whether we’re a dog or a deer or a cow or a human. That may be how they discriminate among potential blood hosts.”

In the study, mosquitoes were put in a wind tunnel that was plain and empty, except for a black dot on the floor to serve as a visual stimulus. The introduction of carbon dioxide into the tunnel triggered the mosquitoes’ instinct to search visually for food, Riffel said.

“When we gave them the odor stimulus, all of the sudden they were attracted to this black dot,” said Riffell. “It’s almost like the carbon dioxide gas turned on the visual stimulus for the mosquitoes to go to this black dot.”

Adding heat to the dot increased the mosquitoes’ attraction to it, Riffel said.

CalTech researcher and first author on the paper Floris Van Breugel told the BBC that to evade mosquitoes’ “annoyingly robust” senses, you would have to “capture all the CO2 that you were breathing out,” dress so you were “visually camouflaged,” and use another person as a distraction.

"The unfortunate conclusion is that it's very difficult to escape mosquitoes,” he said.

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