Chalkhill Blue (Polyommatus coridon, Poda, 1761): Male butterfly photographed in visible and ultraviolet light.

Polyommatus coridon is a butterfly of the family Lycanidae. This species has a Palaearctic distribution. It requires habitats with calcareous soil where the plant Hippocrepis comosa (Fabaceae) can grow, since the caterpillars feed on the latter.
Many butterfly eyes, like in other insect groups are sensitive to UV-light. Therefore, the UV-reflection of their wings might play a role in their intra-species signalling. There is also literature evidence for that hypothesis, e.g. Knüttel and Fiedler (2000).
In this P. coridon the UV pattern on the outside of the wings is dominated by a pretty low reflection. The legs and hairs of the head and body are significantly more reflective. On the other hand, the inner sides of the wings which appear blue in human vision, and are only visible when the animal is active, are much more UV-reflective. The same is true for the outside part of the first wing that is hidden, when the wings are folded and the animal is resting.
So a working hypothesis could be that the outside has sort of an UV-camouflage, while the blue colour of the wing that is only found in males has a signalling function reaching into the UV-spectrum.

Photographed near Burgarach, Southern France 1 & 8 August 2013.
 
All UV-images were taken with a broadband-modified Panasonic Lumix G1 and the EL-Nikkor 80mm/f5.6 at f8.



Visible light image: Panasonic Lumix GH2 (unmodified) with Tokina AT-X 90 mm Macro. (resting animal, outside of the wings):

image reference: CHA_P1200183_130801


Visible light image: Panasonic Lumix GH2 (unmodified) with Tokina AT-X 90 mm Macro. (active animal, inner side of the wings):

image reference: CHA_P1200639_130808

UV-image, Baader U-filter 2”, ISO 400, UV-flash MR21N, (resting animal, outside of the wings):

image reference: CHA_P1100363_130801

UV-image, Baader U-filter 2”, ISO 400, UV-flash MR21N, (active animal)

image reference: CHA_P1100686_130808

UV-image, Baader U-filter 2”, ISO 400, UV-flash MR21N, (active animal)

image reference: CHA_P1100689_130808

Literature:
Helge Knüttel and Konrad Fiedler: On the use of ultraviolet photography and ultraviolet wing patterns in butterfly morphology and toaxonomy: Journal of the Lepidopterists' Society 54(4), 2000, 137-144.