Why So Blue?

Male Common Blue Damselfly, Enallagma cyathigerium

The iridescent turquoise colour of the male Common Blue Damselfly (Enallagma cyathigerium) is a most enchanting thing to behold. It is common throughout Europe and in Ireland is the most frequently encountered damselfly. This is especially the case at this time of year, when individuals are at their most active (and will continue to be so until early August) around open and still waters. E. cyathigerium is especially characteristic of ponds and lakes with large areas of open water and beds of submerged vegetation. Its abundance in Ireland can in part be attributed to its greater tolerance of exposed, open shores as well as highly eutrophic lakes in comparison to other odonate species (1).
E. cyathigerium males' radiant blue comes from the interference and coherent reflection of light from photonic crystals in its cuticular epidermis (2). The colour is at its most conspicuous against surrounding aquatic vegetation during midday and it is at this time that E. cyathigerium is most active (3). Other Enallagma spp. with different colurs (red, yellow) are similarly most active in the evening when low sun angles provided the most contrast. It has been proposed that this The role of such an ability to stand allows males to distinguish both sexually and specifically between individuals (3).

References:

1. Nelson and Thompson, 2004. The Natural History of Ireland's Dragonflies pp. 128-135
2. Prum et al., 2004. Journal of Experimental Biology 207 pp. 3999-4009
3. Schultz et al., 2008. Animal Behaviour 76 pp. 1357-1364