The picture above (taken by Heather Proctor) is a tandem pair of a small coenagrionid damselfly known as Nehalennia irene. The male is blue and green in colour and is above the female. His superior and inferior appendages are holding onto the hind margin of the female’s prothorax (right behind her head which is mostly just eyes). These individuals might have already mated or were about to do so before the photograph was taken. It is relatively clear in this picture even that the males and females of this species look different. However, males also pair with females that look very similar to them (known variously as andromorphs or androchromatypes). Those females can make up < 2% to >95% of the females in a population according to research done largely by Hans Van Gossum, with input from myself and Tom Sherratt. Why is this so? What maintains female morphs at relatively low or high frequencies in different regions or populations? Exciting stuff really.
Professor & student