Mosquitoes Use Infrared Sensing to Find Human Hosts

Mosquitoes seem to find humans irresistible. Beyond our scent and breath, bare skin effectively acts as a glowing signal that a blood meal is available.

A new study suggests this is because mosquitoes can detect infrared radiation through their antennae, helping them locate potential prey.

In 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 - transmitted by the Anopheles gambiae mosquito - caused more than 600,000 deaths in 2022.

Whether the aim is to avoid a severe illness or simply relentless itching, people have strong reasons to prevent mosquito bites.

How mosquitoes use infrared sensing to find people

Scientists led by researchers at the University of California Santa Barbara (UCSB) found that mosquitoes use infrared detection alongside recognised signals, including the CO₂ in human breath and specific 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 vision is relatively poor, while scents may be less dependable in windy conditions or when a host is moving. The researchers therefore proposed that infrared detection could give these insects a consistent way to locate food.

Testing female mosquitoes and simulated hosts

Since only female mosquitoes consume blood, the team placed 80 female mosquitoes, aged about 1–3 weeks, in each cage. They exposed them to different dummy ‘hosts’, created with combinations of thermoelectric plates, CO₂ at the level found in human breath, and human odours. Five-minute videos recorded the insects’ host-seeking behaviour.

The researchers 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."

Some mosquitoes encountered a thermoelectric plate set to 34 degrees Celsius, the average temperature of human skin and a source of infrared radiation. Others were given a plate at an ambient 29.5 °C - a temperature known to appeal to mosquitoes, but one that does not emit infrared radiation.

On their own, none of the individual signals - CO₂, odour or infrared - sparked the mosquitoes’ interest. However, adding infrared to a setup already containing CO₂ and odour 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.

Antennae, exposed skin and mosquito defences

The team further established that the mosquitoes’ infrared sensors are located in their antennae. These contain TRPA1, a protein that responds to temperature. When the researchers removed the gene responsible for this protein, the mosquitoes could no longer detect infrared radiation.

The results may explain why mosquitoes appear especially attracted to uncovered skin. They also help account for the effectiveness of loose clothing, as infrared radiation is dispersed through the fabric, creating an effective invisibility cloak against the insects.

The work could also support more technologically advanced mosquito defences, including traps designed to lure insects using thermal radiation at skin temperature.

"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."

This research is published in Nature.