Mosquito larvae launch their heads like tiny harpoons to catch prey, video reveals

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How do mosquito larvae capture their prey? Using their head.

In attacks too quick to see with the naked eye, the predatory aquatic larvae, which measure about 0.75 inches (2 centimeters) long, launch their heads towards their victims like tiny harpoons, footage filmed at great speed.

During a decades-long investigation, scientists filmed larvae in three mosquito species by consuming their prey. The results, published on October 4 in the journal Annals of the Entomological Society of America (opens in a new tab)revealed that two of these species — Toxorhynchites amboinensis and Psorophora ciliata – could launch their head to grab a target meal in about 15 milliseconds. And in a surprise twist, the researchers found that rapid prey scavenging also occurs in Sabethes cyaneusa species of mosquito whose larvae are mainly passive filter feeders.

“They used their siphons to grab prey larvae and pull them into their gaping mouthparts,” said the study’s lead author. Robert Hancock (opens in a new tab), a professor in the Department of Biology at Metropolitan State University in Denver. “It was one of those ‘I can’t believe this, it’s unbelievable’ moments.”

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Hancock first observed this hunting prowess at a glance and you’ll miss it decades ago in a medical entomology class he attended as a graduate student under co-author of the study Wooded Foster (opens in a new tab), who is now a professor emeritus in the Department of Evolution, Ecology, and Organismal Biology at Ohio State University in Columbus. In this class, as T. amboinensis the larvae reacted to the prey, the students observed the larvae under a microscope – or at least they tried.

“We all saw a blur and then we saw a captured larva being shoveled into a predator’s mouth. That’s all we saw,” Hancock told Live Science. The next step, which would take over 20 years to complete, was to find out what the predators did and how they did it.

This very first glimpse of hunting grubs in action has revealed details of how these tiny predators extend their heads to catch fast-moving prey. (Image credit: originally published in Hancock et al 2022, Annals of the Entomological Society of America, CC BY 4.0)

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Hancock and his co-writers began filming experiments with T. amboinensis and P. ciliate in the 1990s, using the fastest optical system available: a 16-millimeter film camera that had been designed for the US military to track missiles. Once the study authors adapted the camera to film through a microscope, they held prey larvae with jeweller’s tweezers to temper the predators, ultimately capturing images of the larvae at 340 frames per second (fps ).

Most of the time, “the predators made a small body movement when the prey was introduced into their environment,” which signaled to the researchers that it was time to hit the camera button, Hancock said.

“Arch body and head twist”

The scientists found that the larvae threw their heads using the thrust of accumulated abdominal pressure, and clusters of tiny brush-like hairs around their heads spread out like fans in “basket-like arrangements” that helped to sweep prey towards the gaping, sharp jaws of predators. wrote the study authors. P. ciliate “typically struck in a straight (axial-linear) fashion,” according to the study, while strikes by T. amboinensis “often involved a lot of arching of the body and twisting of the head.”

“All scientists are excited about their discoveries, but this kind of science — these visual discoveries — is special,” Hancock said.

Shooting S. cyaneus larvae at up to 4,352 frames per second showed them capturing prey with rapid tail movements – an unexpected strategy for larvae that primarily feed on filters. (Image credit: originally published in Hancock et al 2022, Annals of the Entomological Society of America, CC BY 4.0)

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But T. amboinensis and P. ciliate the larvae are active predators, and scientists have wondered if similar methods could be used by species that combine hunting with filter feeding. After funding ended, the project was put on hold until 2020, when the researchers were finally able to come back to this issue. This time they used a high definition video camera capable of shooting up to 4352 fps, with which they recorded S. cyaneus the larvae in specially designed “arenas” for death.

The predatory action they saw, in which the larvae used their tails to quickly sweep their prey into their waiting mouths, was also previously unknown; like head-throwing strikes, hunting with tail sweeps took about 15 milliseconds from start to finish and was “spectacular,” Hancock said. Once S. cyaneus seized its victim, the larvae’s mandibles “opened and closed so that their serrated teeth tore the prey apart,” according to the study.

Future studies could explore how common spearhead hunting and tail-swiping are in the mosquito lineage, by “putting my cameras on as many different types of mosquitoes as possible,” Hancock said. “There’s a much bigger story to tell.”

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