A kind of adolescent mosquito can suddenly throw its head forward from its body – stretching its neck in a thin rope – to bite into another youngster. And that’s just one of the ways young mosquitoes kill other mosquitoes, according to a new study.
For decades, scientist and cinematographer Robert Hancock and his colleagues have filmed the attacks of these Psorophora ciliata and two other types of predatory mosquito larvae with unusual detail. The throwing heads evolved independently into two of the types, according to him and his colleagues in their new study.
The third predator, a kind of Sabethes mosquito larva, uses its other end. Suspended upside down in the water, it only needs 15 milliseconds grab the prey with a hooking sweep of the breathing tube on its predatory buttresearchers report on October 4 to Annals of the Entomological Society of America.
Perhaps the most dramatic leap on film is the ripping of the neck by the Psorophore larva. It could feed this cleft by pressing a surge of liquid towards the head. When Hancock observes the mosquito’s body, segmented much like a string of alphabet beads, he can see two segments crumpling inwards “accordion-like”, as if squirting liquid forward when the head springs.
Throwing the head to reach the prey is one thing, but grabbing it is another problem. The newly released video gives a clear view of a pair of brushes, one on each side of the head, which help with grip. As the head approaches its victim, the brushes fan out in what researchers call a “fragile basket-like arrangement” that curls around the doomed prey.
Such an attack may surprise people thinking of mosquito bites just like stealthy hypodermic bloodsuckers. It is the adult bite of females who crave a nutritional supplement for egg laying. Mosquito eggs, however, hatch in water and the larvae do not assume their flying dandelion form for weeks. During the aquatic phase, these larvae do not resemble the adult forms at all and do not eat them at all.
The larvae do not bite people, and many simply filter edible crumbs that float in the water. Meat eaters, however, leap so fast that the human brain cannot analyze them. Hancock has been fascinated since he was in a classroom in the 1980s, seeing only a blur through the microscope as he tried to describe eating behavior. The Toxorhynchitis the mosquitoes that then frustrated him turned out to be one of the groups that developed head-throwing larvae.
“If there’s one mosquito that everyone who hates mosquitoes might not like, but like, it’s Toxorhynchitissays Hancock, now at Metropolitan State University in Denver. As iridescent adults, they are vegan and feed primarily on flower nectar. For larvae, it’s just meat, mostly other mosquitoes. Plus, he says, “They’re big and they’re gorgeous.”
The new study found that the launch does not extend to the length of the head, but Toxorhynchitis vigorously attacks the larva prey. In the videos, “the moment you saw him, there would be like half a larva…because he pushed this thing like it was a hot dog eating contest,” Hancock says.
He and his colleagues also filmed a third type of carnivorous mosquito, Sabethes, which are more flexitarian than carnivorous. They always eat their meat from the side of the head, but the danger of getting caught comes from behind, researchers’ videos show. Like many mosquito larvae, they often hang their heads in the water, taking in oxygen through a flexible siphon. It turns out that the breathing tube doubles as a type of food hook, capable of grabbing a target in just milliseconds.
“The thing about Sabethes it’s that they probably look more like killers because they don’t ingest and consume whole prey larvae like the other two,” says Hancock. Feeding tests show that insects get at least some food from nibbling.
A human watching the grub hunt might wonder why we put so much money and chemistry into trying to kill the pests when their own little relatives do it so brilliantly. For one thing, mosquito larvae stay underwater, says entomologist Don Yee of the University of Southern Mississippi at Hattiesburg, who was not involved in the study. Both sets of stretchers cannot rise into the air and fly to the next water-filled tire or tree hole. There, a Toxorhynchitis, for example, “would probably consume all the other larvae,” he says. “[H]However, there may be hundreds of such containers in the region.
In contrast, stretching the neck Psorophore mosquitoes live in larger bodies of water and could theoretically have more of an effect in reducing mosquito numbers, Yee says. But under natural circumstances, predators are unlikely to crush mosquito populations as humans would like. Yee compares it to the African savannah. In the photos, “you can see how many wildebeest there are. Lions can’t really control them. In nature, after all, thriving predators do not eliminate their own prey.