Male mosquitoes recognize females by sound. Current Biology:

Scientists have discovered that insects chase others only when they hear the hum of a female.

Male mosquitoes form swarms of thousands to attract potential mates, but must avoid each other when pursuing females. Dr. Saumya Gupta of the University of Washington in Seattle says that mosquitoes were previously thought to have such poor vision that they could not see each other.

Furthermore, male mosquitoes are known not to pick up on the sounds made by other males, meaning they cannot rely on their own hearing to avoid collisions. Now Gupta and his colleagues have shed light on how insects do this.

"Not only did we find that (mosquitoes) can see the visual cues of other mosquitoes flying around," says Gupta, "but we also found that male mosquitoes can actually combine acoustic cues with visual cues (to search for a female).

In a paper published in the journal Current Biology, Gupta and his colleagues described how they kept mosquitoes in an enclosure covered with an LED panel that reflected a constant pattern of bright pixels.

That, scientists say, mimics what a mosquito might see in a swarm. The team of scientists then attached a large moving dot of light to an LED display to represent another mosquito flying right next to it.

The researchers found that the mosquitoes showed no desire to approach or move away from the large mosquito, even though the scientists varied the frequency and amplitude of the wing flaps, the magnitude of the oscillation. However, when the ear-piercing buzzing of the female was heard, the male mosquitoes resolutely turned in the indicated direction.

"As soon as they hear the female mosquitoes making sounds, they try to catch the object," says Gupta.

In other words, the sound made by the female mosquito appears to trigger a shift in the visual processing of the male mosquito.