Praying mantis: unique stereoscopic vision
We have two eyes, i.e. binocular vision, so we can see ‘depth’, or a three-dimensional picture, called stereopsis. With one eye, we would have only a two-dimensional image, but our two eyes have two slightly different images. From these differences, the brain computes distances to the different objects, building a 3D picture.
Now it turns out that the big eyes on the triangular head of the praying mantis also produce stereopsis. This comes in handy when working out whether it can capture its prey with its lightning-fast spiked forelegs.1
However, the mantis stereopsis is very different from that of humans. Instead of comparing two static images, the mantis compares the way the two images change.2 In experimental tests, the mantises sometimes performed better than humans at judging distances to moving objects, such as when the two images had very different brightnesses, or when the images were not clear. But mantises can’t judge the distances to stationary objects, so they strike only moving prey.
Like that of humans, the praying mantis’ stereopsis requires brain processing. But this method must use very efficient computational processing so that it can be performed in an insect’s tiny brain. The mantis brain has only about a million neurons, whereas the human brain has about 100 billion.
References and notes
- Insects are probably not biblically alive, in the sense of nephesh chayyah (living creatures), but are ‘God’s robots’. But after the Fall, mantises have been known to eat nephesh chayyah such as hummingbirds. See creation.com/nephesh-chayyah. Return to text.
- Nityananda, V. and five others, A novel form of stereo vision in the praying mantis, Current Biology 28:1–6, 19 February 2018 | doi:10.1016/j.cub.2018.01.012. Return to text.