The Blue Triangle Butterfly

The Blue Triangle butterfly, Graphium sarpedon has been the star research subject in Japan.

All butterflies see colours like we do, plus they also see ultraviolet and polarized light. However, recent studies in Japan of the Blue Triangle butterflies have found each of their eyes have at least 15 different types of photo receptors.

Most insect species have only three classes of photoreceptors. Even humans have only three cones, yet we still see millions of colours. Butterflies need only four receptor classes for colour vision, including the UV spectrum.

They found that different colours stimulate each class of receptor. For instance, UV light stimulates one, while slightly different blue lights set off three others; and green lights trigger four more.

So why did this species evolve 11 more? The scientists suspect that some of the receptors must be tuned to perceive specific things of great ecological importance to these iridescent butterflies—such as sex. For instance, with eyes alert to the slightest variation in the blue-green spectrum, male bluebottles can spot and chase their rivals, even when they’re flying against a blue sky.