Drosophila: D. hydei (the larger, dark flies) and D. melanogaster and D. simulans (the smaller, lighter flies) interacting at a food source. Although there is little sexual dimorphism between males and females of the D. hydei species, males can be distinguished in the video because they approach other flies to court. In the D. melanogaster and D. simulans species, males are smaller than the females and have darker abdomens. These males can also be seen approaching other flies and attempting to court. Attempted courtships are brief and often end when females extrude their ovipositors. Notice that males will approach flies of different sexes and species, and that flies of D. hydei are much less active than those of D. simulans and D. melanogaster. D. melanogaster and D. simulans are sibling species and are morphologically indistinguishable in this video. Video credit: Therese Ann Markow.