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Scientists gave praying mantises tiny 3D glasses to test their depth perception

James Vincent

Pretty much everything we know about stereopsis, or 3D vision, we've learned from vertebrates. Monkeys, cats, owls, and toads have all been the subject of research showing that these animals have the ability to compare images from different eyes to perceive depth. But the same ability has only been demonstrated in one invertebrate, the mantis. To build on this research and find out more about how the insects might have evolved stereopsis independently from vertebrates, scientists from Newcastle University did the only sensible thing: they gave mantises tiny 3D glasses and made them watch films of moving targets to see if they reacted. It worked.

Beeswax and freezers: essentials for any insect optician

In a paper published in Scientific Reports, an open access journal from Nature, the scientists explain that they initially tried testing the mantises' vision using circularly polarized 3D glasses like you get in the cinema. (Some of this early work was publicized back in 2014.) But this method failed, because the mantises were too close to the screen for the 3D effect to work, notes Popular Mechanics. Instead, the scientists moved onto to spectral 3D glasses — like the old-school ones that use red and blue lenses. Because mantises don't see so well in red light, though, they switched to green and blue lenses, immobilizing the insects by placing them in a freezer for a few minutes and them holding them in place using modeling clay. The mantises were then fitted with their new 3D specs, which were stuck on with a combination of beeswax and pine resin. (No one ever said being an insect optician was going to be easy.)

"My eyes! The goggles do nothing!" (Image credit: Newcastle University)

The mantises were then shuffled into a "3D insect cinema" and shown computer-generated images of different targets moving toward them. The colors of the targets were varied in different trials and the mantises were monitored to see when — if at all — they struck out with their forelimbs to try and "capture the perceived prey." The results? "Clear and dramatic proof of stereopsis in insects," write the researchers, noting that their new technique for study "opens up broad new avenues of research" in insect vision.

"Despite their minute brains, mantises are sophisticated visual hunters which can capture prey with terrifying efficiency," said Jenny Read, a professor of vision science at Newcastle University, in a press release. She added that, "better understanding of their simpler processing systems helps us understand how 3D vision evolved, and could lead to possible new algorithms for 3D depth perception in computers." And all it took was patience and a little bit of beeswax.

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