National Geographic : 1959 Apr
KODACHROMEBY CONSTANCEP. WARNER© NATIONALGEOGRAPHICSOCIETY Horsefly's Monstrous Eye Transmits 7,000 Separate Pictures to the Brain Swift insects, like fast birds, possess large eyes. This male's upper facets (magnified 25 times) project bright but coarse images of the world above him; smaller units below convey less light but finer detail. He feeds only on nectar and plant juices. The female horsefly, which sucks blood, lacks the male's "bifocal" vision. Powered by a hundred wing beats a second, she can overtake any horse. Each facet in the eyes of 566 both sexes transmits a fragment of the total picture-a single tile in a living mosaic.