Greatest eye span (relative to body size)

To increase their binocular vision, a number of animals including snails, lobsters and crabs have evolved stalked eyes – or "ocular peduncles". However, the animals with the longest eyestalks and span between their eyes, relative to body size, are the stalk-eyed flies (Diopsidae). In some species of this fly family, the distance between the eyes can even exceed their body length. One large male specimen of the Malayan stalk-eyed fly (Cyrtodiopsis whitei) – a species native to the Indian subcontinent and south-east Asia – had a body length of 7.5 millimetres (0.29 inches) and a span between its eyes of 10.5 millimetres (0.41 inches) – equating to an eye span to body length ratio of 1.4.

In terms of eye span, the Malayan stalk-eyed fly exhibits sexual dimorphism, with male eyestalks typically measuring much longer than those of females.

Studies have shown that eyestalk length/eye span also plays a key role in attracting a mate among stalk-eyed flies and may be an indication of genetic quality.