If the female African mantis (Sphodromantis lineola) pictured above wearing teensy 3D glasses looks like she’s on her way to the movies, that’s because she is. But it wasn’t just insect dress-up time in the laboratory. The minuscule specs and movie theater were an experiment to find out if mantises can see in three dimensions.
The idea of not being able to see 3D sounds pretty weird, but scientists say stereoscopic, or 3D, vision is actually pretty rare in the animal kingdom. Humans have it (most humans, anyway), as do other primates, horses, birds, cats, and toads. However, it’s generally believed that invertebrates like bugs see the world in only two dimensions. To date, only one invertebrate has been shown to possess stereoscopic vision: the praying mantis.
The original mantis vision experiment occurred in the 1980s. At the time, the researcher was pretty limited in the 3D images he could create. More than 20 years later, 3D technology is everywhere, and a team of researchers figured they could build a pretty decent mantis movie theater. For science.
Scientists Vivek Nityananda, Ghaith Tarawneh, Ronny Rosner, Judith Nicolas, Stuart Crichton, and Jenny Read outlined their methods and findings in a paper published yesterday in Scientific Reports. The first step was to make a movie that would interest a mantis audience. They opted for an animation of a spiraling disc against a brightly colored background. The disc bounced around the screen, occasionally hovering in place—a bug-like movement pattern that has been shown to keep the mantises’ attention and even provoked them to strike. They set the animation to play on a high-resolution computer monitor and constructed a small black tunnel to limit the size of the screen.
Next, they cut out little circles from blue and green plastic filters. They stuck the mantises briefly in a freezer to sedate them, then pulled them out and affixed the 3D glasses to their faces with beeswax and rosin. Looking like extras in a B-52s video, the mantises then went back to their cages to recover from the weirdness they’d just experienced.
Image credit: Newcastle University
The next day, the researchers took out the newly bespectacled bugs and brought them to the little movie theater. They set them in front of the tunnel and recorded how many times the mantises tried to strike the images they saw on the screen.
The results confirm the mantises’ use of 3D vision. When the target was rendered in three dimensions and seemed to pop off the screen, the mantises lunged for it. When it was 2D, they didn’t show much interest.
The research team was pleased with their results. "Despite their minute brains, mantises are sophisticated visual hunters which can capture prey with terrifying efficiency,” lead researcher Jenny Reed said in a press statement. “We can learn a lot by studying how they perceive the world.”