To distinguish between male and female fruit flies, look at the fly to see if it has stripes, which is a sign that it's a female. If you can compare 2 flies, note that the larger fly will be female as they have longer abdomens. You should also loo out for a pointed abdomen on a female fly and a blunt abdomen on a male fly. Additionally, look for bristles on the fly's forelegs, which is a sign it's a male. Alternatively, watch out for males hopping when they prepare to mate, and females standing still.