Mosquitoes prefer biting humans wearing red, orange or black clothes

SEATTLE — Pesky mosquitoes are more attracted to people who wear red, orange or black clothes, according to scientists. If you’re looking to keep them away, your outfit better have plenty of green, purple, blue or white. You’ll also need to cover up, though, as any color of human skin appears red to them.

Findings from the study out of the University of Washington could help us steer clear of the annoying pests and their itchy bites. Not to mention, they can further help avoid potentially contracting Zika or West Nile viruses, along with other mosquito-borne illnesses.

Scientist say the insects fly towards specific colors once they have smelled a plume of CO2 from human breath. Once they catch a whiff, they zero-in on particular hues that catch their fancy. Avoiding the blood-suckers this spring and summer may hinge on the right choice of attire to cover your skin.

“Mosquitoes appear to use odors to help them distinguish what is nearby, like a host to bite,” says study senior author Jeffrey Riffell, a professor of biology at the university, in a statement. “When they smell specific compounds, like CO2 from our breath, that scent stimulates the eyes to scan for specific colors and other visual patterns, which are associated with a potential host, and head to them.”

Colorful findings may lead to better mosquito repellants

The findings shed some light on why mosquitoes attack some individuals, and leave others alone. In addition to red, orange, and black, they also enjoy other colors like aqua and cyan. Human skin, regardless of overall pigmentation, emits a strong red-orange “signal” to the insects’ eyes. Its sense of smell, or olfaction, influences how it responds to visual cues.

Knowing what lures the hungry pests also opens the door to developing better mosquito repellents, traps and other methods to keep them at bay. “One of the most common questions I’m asked is ‘What can I do to stop mosquitoes from biting me?'” says Riffell. “I used to say there are three major cues that attract mosquitoes: your breath, your sweat and the temperature of your skin. In this study, we found a fourth cue: the color red, which can not only be found on your clothes, but is also found in everyone’s skin. The shade of your skin doesn’t matter, we are all giving off a strong red signature. Filtering out those attractive colors in our skin, or wearing clothes that avoid those colors, could be another way to prevent a mosquito biting.”

For the study, Riffell and his team tracked the behavior of female Aedes aegypti mosquitoes in a test chamber when exposed to visual and scent cues. Like all mosquito species, only females drink blood. Bites from A. aegypti can transmit dengue, yellow fever, chikungunya, and Zika.

Specific odors were sprayed. Patterns such as a colored dot or a tasty human hand were also presented. Without any fragrance stimulus, the insects largely ignored the mark at the bottom of the chamber, regardless of color. After a spritz of CO2, they continued to pay no attention if it was green, blue or purple.

But they headed straight for the dot when it was red, orange, black or cyan.

It’s mostly about how you smell — but colors can keep the pests away

Humans can’t smell CO2, which we and other animals exhale with each breath. Mosquitoes can. Previous research has shown it boosts females’ activity, making them explore surrounding space in search of a host. The latest study reveals that after sniffing the gas, their eyes prefer certain wavelengths in the visual spectrum.

It is similar to what might happen when humans smell something good.

“Imagine you are on a sidewalk and you smell pie crust and cinnamon. That is probably a sign there is a bakery nearby, and you might start looking around for it,” says Riffell. “Here, we started to learn what visual elements that mosquitoes are looking for after smelling their own version of a bakery.”

Most humans have “true color” vision. We see different wavelengths of light as distinct colors. For example, 650 nanometers shows up as red while 450 wavelengths look blue. The researchers do not know whether mosquitoes perceive colors the same way.

But most of those the mosquitoes preferred – orange, red and black – correspond to longer wavelengths of light. Human skin also gives off a long-wavelength signal in the red-orange range.

When the trials were repeated with human skin tone pigmentation cards, or a researcher’s bare hand, mosquitoes again flew toward the visual stimulus only after CO2 was introduced. If filters removed long-wavelength signals, or a green-colored glove was worn, they did not.

Mosquitoes with a mutation needed to smell CO2 no longer showed a color preference. Another strain of mutant mosquitoes, with a change related to vision so they could not ‘see’ long wavelengths of light, were more color-blind in the presence of CO2.

“These experiments lay out the first steps mosquitoes use to find hosts,” says Riffell

More research is needed to determine how other visual and odor cues, such as skin secretions, help mosquitoes target potential hosts at close range. Other mosquito species may also have different color preferences, based on their preferred host species. But the new findings add a colorful new layer to mosquito control.

The study is published in the journal in Nature Communications.

South West News Service writer Mark Waghorn contributed to this report.