The holly blue is a familiar garden sight, even within the boundaries of cities. In fact, I have seen it in some numbers from trains in London, flying over the ivy banks that often straggle near the railsides. Both sexes are unmistakeable once the 'jizz' has been learned. The very white underside, with a washing-powder 'blue-whiteness', colours the insect even in flight, and the upperside too is distinctive, though different in the two sexes. The female always has a very broad dark border to the forewing, broader in the second, summer brood, unlike anything found in any other species. The male, when fresh, shows a broadening of the narrow border near the apex of the wing and also chequering to the margins, but neither of these is visible in worn insects.

In England, the first brood of this butterfly feeds on the fresh, new leaves of holly, while the second brood feeds on ivy. Anywhere (in the south) where both these plants grow you are likely to find holly blues. On the continent, apparently (I learned recently), they are not so regimented and will feed on either plant throughout the season.