Tim writes: Apart from being the sole European representative of a tropical family of butterflies, Duke of Burgundy has another unusual attribute. Males and females have a different number of legs. Everyone knows that all insects have six legs, but sometimes they are reduced to become vestigial appendages, hardly visible at all. This is exactly what has happened to the front pair of legs in male Duke of Burgundy, while the female has a normal front pair of legs. This is clearly visible in this photograph with the four-legged male on the left, and the six-legged female on the right.
I photographed this mating pair in North Yorkshire
Taken with Nikon D7000 Nikkor 105mm f2.8 set at f10 1/1000 ISO 800