Their heads are subtriangular, with transverse eye stalks in all genera except the African genus Centrioncus and Teloglabrus.

Adult males have lost tergites seven and eight, and the seventh sternite forms a complete ventral band.

Their eyes are mounted on projections from the sides of the head, and the antennae are located on the eyestalks, unlike stalk-eyed flies from other families.

[8] A rather remarkable feature of stalk-eyed flies is their ability, shortly after they emerge from their pupae, to ingest air through their oral cavity and pump it through ducts in the head to the tips of the eye stalks, thereby elongating them while they are still soft and transparent.

[9] True stalk-eyed flies are members of the family Diopsidae, first described by Fothergill,[10] with the genus Diopsis named by Carl Linnaeus in 1775.

[11] The family Diopsidae is contained within the order Diptera and suborder Cyclorrhapha;[12] it is divided into two subfamilies: The African genus Centrioncus (once placed in Sepsidae, but then moved to Diopsidae) was once recommended to be treated as a separate family, Centrioncidae, a sister group of the diopsids,[13] but since then this lineage has usually been treated as a subfamily.

At dusk, the animals gather in small groups on selected thread-like structures, returning to the same site each day.

This contest involves males facing one another and comparing their relative eye spans, often with the front legs spread apart, possibly to emphasize their eye-stalk lengths.

[22][23] This process creates linkage disequilibrium between selected alleles, with the magnitude of resulting genetic correlations influencing evolutionary outcomes.

From January to October, the researchers counted males and females on 40 root hairs along a single 200-m stretch of stream bank to confirm this observation.

Test males with the longest or shortest eye-span to body-length ratios were mated with 25 randomly chosen females.

[27][28][29][30][31] Genetic variation underlies the response to environmental stress, such as variable food quality, of male sexual ornaments, such as the increased eye span, in the stalk-eyed fly.

Unlike these characteristics, male eye span still reveals genetic variation in response to environmental stress after accounting for differences in body size.

Thus, it could be inferred that these results strongly support the conclusion that female mate choice yields genetic benefits for offspring as eye span acts as a truthful indicator of male fitness.

[26] Furthermore, some populations of stalk-eyed fly females carry a meiotic drive gene on their X chromosomes that causes female-biased sex ratios.