The Common Horse Fly (Haematopota pluvialis)
Horse flies mainly eat nectar from flowers, but females require a hearty drink of some other creature’s blood to fortify themselves before laying eggs.
Their unusual compound eyes – each one composed of thousands of independent lens-and-receptor units – allow them to see the polarisation of light. They are attracted to the horizontally polarised light reflected off water, which makes them a common poolside pest.
Compound eyes have poor resolution compared to the single-aperture eyes with which you are likely reading this. They can cover a wide angle of view, however, and catch movement very quickly.
In addition to its large compound eyes, the damselfly has three light-sensors called ocelli on top of its head, which can’t form images but are very sensitive to light intensity and may be used to maintain stability while flying.
Mantis Shrimp (Stomatopoda)
Mantis shrimp have extremely elaborate eyes. They contain 16 different colour-receptive cones to see a wide spectrum of light. Each eye moves independently on its stalk and can capture three separate images of whatever it is looking at.
Jumping spider (Salticidae)
Spiders’ eyes aren’t compound, but they do have eight of them. The front pair have the best resolution and can be moved around, while the other three pairs are fixed and can’t see as sharply.
Jumping spiders are expert hunters and have quite acute vision in a narrow area which they scan around to build a picture of their surroundings. They have four colour receptors and can see into the ultraviolet spectrum. For depth perception, they compare the relative fuzziness of out-of-focus parts of an image to determine the distance to different objects.