A zebra grazes in the African savanna, surrounded by a cloud of flies — horseflies, tsetse flies, and mosquitoes. But instead of landing calmly, the insects jerk, miss their target, and crash into the hide. The reason is not camouflage but the structure of the fly's eye.
The horsefly's eye is a mosaic of thousands of tiny tubes, ommatidia, each pointing in a different direction. As the fly approaches the striped hide, its ommatidia begin to "argue" with the stripes. A moiré effect arises, like when you overlay two fine grids and see floating patterns. In the insect's eye, false stripes are born that don't actually exist. These phantoms confuse the motion detectors, and the fly loses its ability to calculate its landing trajectory.
But there's more. In the fly's brain, there is a layer that compares signals from neighboring ommatidia and computes motion. The false stripes deceive this layer, generating phantom velocity vectors. The fly thinks the target is slipping sideways and tries to correct its course, but all in vain. Thus, the simple geometry of stripes becomes a reliable shield against bloodsuckers.
A horsefly sees the world at about 200 frames per second — for it, our smooth movements look like slow motion.