I have been chasing this chap all over the “football pitch” today. It is pretty windy so he does not sit still for long….
The common blue butterfly or European common blue (Polyommatus icarus) is a butterfly in the family Lycaenidae and subfamily Polyommatinae. The butterfly is found throughout the Palearctic. Butterflies in the Polyommatinae are collectively called blues, from the coloring of the wings. Common blue males usually have wings that are blue above with a black-brown border and a white fringe. The females are usually brown above with a blue dusting and orange spots.
Polyommatus icarus has a wingspan of 28–36 millimetres (1.1–1.4 in). The dorsal side of the wings is an iridescent lilac blue, bright violet-blue, or almost hyacinth-blue with a thin black border. Females’ wings are brown or black-brown with a row of red reddish yellow spots along the edges of the wings (marginal spots) and usually some blue at the base. The extent of blue and brown is extremely variable depending on location. The top of the wings in the female may be mostly blue, especially in Ireland and Scotland, but it always has red spots. The ventral side has a greyish or dust-grey base colour in the males and a more brownish hue in the females. Both sexes have a row of red or orange spots along the edge of the hindwing and extending onto the forewing, though they are generally fainter there, particularly in the males, where they are sometimes missing altogether. There are about a dozen black-centered white spots (ocelli) on the hindwing and nine on the forewing. These usually include one in the middle of the forewing cell, absent in Chapman’s and Escher’s blues. The fringes on the outer edge of the wings are uniform white, not crossed with black lines as in the chalkhill and Adonis blues (that is, the common blue lacks checkering).
Common blues sequester flavonoids from their host plants and allocate these pigments that are UV-absorbing into their wings. These flavonoid pigments in females attract males. Males who patrol areas of suitable habitats while searching for virgin females stop and inspect females who have flavonoid pigments in them. This may be due to the fact that flavonoid pigments that have UV absorption increase color saturation on females and allow females to be more conspicuous.There are also some other advantages of sequestering flavonoids, including the protection of eggs from adverse UV chemical reactions, as the butterflies will absorb the UV rays, and the flavonoids can offer a chemical defense against predators or pathogens.
Flavonoid sequestration is much more effective when coming from natural host plants than from experimentally offered diets. Females sequester about 60% more flavonoids than do males. This richness in females may increase visibility, but could also confer information about feeding history, and consequentially the quality of potential mate. Flavonoid sequestration is an important component of intraspecific visual communication and sexual signaling in Polyommatus butterflies.
Visual systems in butterflies are highly diverse and their color vision abilities have only begun to be explored. To see color, P. icarus uses a duplicated blue opsin in conjunction with its long-wavelength opsin LWRh. This enables the common blue to see color in the green part of the light spectrum extending up to 560 nm (2.2×10−5 in). There is also a difference between the dorsal and ventral eye-shine of P. icarus, with the dorsal retina dominated by yellow-reflecting ommatidia and the ventral exhibiting yellow and red-reflecting ommatidia. P. icarus is able to use color vision and distinguish between yellow of 590 nm (2.3×10−5 in) and blue of 430 nm (1.7×10−5 in), but is not able to distinguish between yellow and red of 640 nm.