The physics of mosquito takeoffs shows why you don’t feel a thing

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Discovering an itchy welt is often a sign you have been duped by one of Earth’s sneakiest creatures — the mosquito.

Scientists have puzzled over how the insects, often laden with two or three times their weight in blood, manage to flee undetected. At least one species of mosquito — Anopheles coluzzii — does so by relying more on lift from its wings than push from its legs to generate the force needed to take off from a host’s skin, researchers report October 18 in the Journal of Experimental Biology.

The mosquitoes’ undetectable departure, which lets them avoid being smacked by an annoyed host, may be part of the reason A. coluzzii so effectively spreads malaria, a parasitic disease that kills hundreds of thousands of people each year.

Researchers knew that mosquito flight is unlike that of other flies (SN Online: 3/29/17). The new study provides “fascinating insight into life immediately after the bite, as the bloodsuckers make their escape,” says Richard Bomphrey, a biomechanist at the Royal Veterinary College of the University of London, who was not involved in the research.

To capture mosquito departures, Sofia Chang of the Animal Flight Laboratory at the University of California, Berkeley and her colleagues set up a flight arena for mosquitoes. Using three high-speed video cameras, the researchers created computer reconstructions of the mosquitoes’ takeoff mechanisms to compare with those of fruit flies.

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Mosquitoes are as fast as fruit flies while flying away but use only about a quarter of the leg force that fruit flies typically use to push off, Chang and her colleagues found. And 61 percent of a mosquito’s takeoff power comes from its wings. As a result, the mosquitoes do not generate enough force on a mammal’s skin to be detected.

Unlike fruit flies’ short legs, mosquitoes’ long legs extend the insects’ push-off time. That lets mosquitoes spread out already-minimal leg force over a longer time frame to reach similar takeoff speeds as fruit flies, the researchers found. This slow and steady mechanism is the same regardless of whether the bloodsuckers sense danger or are leaving of their own accord, and whether they are full of blood or have yet to get a meal. While in flight, though, a belly full of blood slowed the mosquitoes down by about 18 percent.

Chang next wants to determine whether mosquitoes land as gently as they depart. “If they are so stealthy when they leave, they must be stealthy as they land, too.”