ON THE BACK:
The common blue is widely distributed throughout the British Isles. This is largely due to its caterpillars feeding on plants that are similarly widespread (the plants are all members of the pea family and include bird’s-foot-trefoil and clover). The bright blue colour of the male is not a pigment but is produced by the diffraction of light by thousands of small scales which absorb all the colours of the spectrum other than blue.