Mosquitoes Use Infrared Sensing to Find Human Hosts

Mosquitoes appear to find us especially appealing. Alongside our scent and the air we exhale, uncovered skin effectively acts like a glowing advert telling them that a blood meal is available.

Mosquitoes use infrared sensing to locate hosts

A new study indicates that mosquitoes track potential prey using infrared sensing in their antennae.

Across much of the world, mosquito bites are not merely irritating: they can transmit pathogens responsible for dengue, yellow fever and Zika virus. According to World Health Organization figures, malaria, which is spread by the Anopheles gambiae mosquito, killed more than 600,000 people in 2022.

Whether the aim is to avoid a dangerous illness or simply the intensely irritating itch, people are understandably eager to prevent mosquito bites.

Scientists led by researchers at the University of California Santa Barbara (UCSB) discovered that mosquitoes rely on infrared detection, alongside known signals including CO₂ in human breath and particular body odours, when searching for hosts.

"The mosquito we study, Aedes aegypti, is exceptionally skilled at finding human hosts," says UCSB molecular biologist Nicholas Debeaubien.

Mosquito eyesight is relatively poor, while odours may be unreliable in windy conditions or when a host is moving. The researchers therefore proposed that infrared detection could give these insects a dependable way to locate food.

Testing infrared detection in Aedes aegypti

Because only female mosquitoes consume blood, the team used cages containing 80 female mosquitoes, each roughly 1–3 weeks old. The insects were offered various dummy “hosts”, created from combinations of thermoelectric plates, CO₂ at the concentration found in human breath, and human odours. The researchers then filmed 5-minute videos to monitor host-seeking behaviour.

They described this behaviour as "a mosquito landing, walking, and extending its proboscis through the mesh of the cage, which is reminiscent of a female landing on a human and then walking while sampling the skin surface with its labellum."

For some mosquitoes, the thermoelectric plate was set to 34 degrees Celsius (93 °F), the average temperature of human skin; it also emitted infrared radiation. Other plates were maintained at the ambient temperature of 29.5 °C, which mosquitoes are known to favour but which produces no infrared.

None of the individual signals - CO₂, odour or infrared - was enough to attract the mosquitoes. However, adding infrared to a setup containing CO₂ and odour alone doubled the insects’ apparent drive to seek blood.

"Any single cue alone doesn't stimulate host-seeking activity. It's only in the context of other cues, such as elevated CO₂ and human odor that IR makes a difference," says UCSB neurobiologist Craig Montell.

The researchers further established that the mosquitoes’ infrared sensors are located in their antennae, which contain the temperature-sensitive protein TRPA1. Once the team removed the gene responsible for this protein, the mosquitoes could no longer sense infrared.

Why exposed skin attracts mosquitoes

These results help account for mosquitoes’ apparent attraction to bare skin. They also explain why loose clothing, which allows infrared radiation to disperse, can work as an effective invisibility cloak against the insects.

The work could also support more technologically advanced mosquito defences, including traps that use thermal radiation at skin temperature to attract mosquitoes.

"Despite their diminutive size, mosquitoes are responsible for more human deaths than any other animal," DeBeaubien says.

"Our research enhances the understanding of how mosquitoes target humans and offers new possibilities for controlling the transmission of mosquito-borne diseases."

The research was published in Nature.