Thousands of tiny eyes stitched into one view
Arthropod compound eyes pack as many as thousands of ommatidia—each a cornea, lens, and photoreceptors sampling brightness and colour. Apposition designs form many inverted images; superposition designs fuse light into one erect picture. Dragonflies and bees sharpen zones into fovea-like acute patches.
Typical apposition eyes focus one direction’s light on a rhabdom while dark walls kill off-axis rays; mantis shrimp exemplify advanced versions. Superposition eyes split into refracting, reflecting, and parabolic subtypes. Refracting forms leave a gap between lens and rhabdom without side walls, redirecting angled rays so many facets feed one image point—useful in dimmer light.
Fast fliers and hunters flatten regions of the eye and enlarge facets, packing more ommatidia onto the same visual angle for acute zones. That geometry trades panoramic sampling for targeting precision where prey or landmarks matter most.
The categories leak. In the twisted-wing insects called Strepsiptera, each lens of an apposition eye forms its own small image rather than a single point. Some insects carry a single-lens compound eye, a halfway design between the many-faceted superposition eye and the simple eye, and the mysid shrimp Dioptromysis paucispinosa pairs a refracting superposition eye with an unusually large lens. The house centipede Scutigera goes the other way: its pseudofaceted eye is a cluster of simple ocelli arranged to mimic the real thing. Asymmetric eyes may even steer behaviour; scouts of the ant Temnothorax albipennis favour left turns when exploring new nest sites, possibly a useful rule in maze-like terrain. One celebrated claim has been retired: the brittle star Ophiomastix wendtii was once thought to be coated in ommatidia, effectively a full-body eye, but its light sensing uses no lenses and forms no image. Humans borrowed the look long ago, too, as knobbly many-coloured glass beads known as dragonfly eyes were made across Asia some 2,000 to 2,500 years ago, and the 2010s brought novels by Wu Ming-yi and Cao Wenxuan named for such eyes.
Source: Compound eye
