How to tell a flies gender?

Two of the most common differences occur on the head. The first is where males have large eyes that may take up most of the head and touch centrally, holoptic.Females on the other hand have normal-sized eyes and are separated by a partition, they are known as dichoptic.The other difference occurs mostly in lower Diptera where male antennae are much more plumose, (fuzzy or feathery), than females who have reduced plumage on their antennae with short hairs. However, it should be said that both of these rules are not universal throughout flies.