Common Blue: This is the familiar blue of the wider countryside and, indeed, is common. The males are a bright sky-blue colour whereas the females may have a lot of blue scales or these blue scales may just be confined to the body so that they look generally brown. It is these brown females which can look like Brown Argus except that the Brown Argus is distinctly smaller and has some differences in the underwing spotting pattern. Mature, 4th instar caterpillars emerge from hibernation in April and pupate. The first-generation adult butterflies will then emerge in May and early June. The fertilised females seek out bird’s foot trefoil on which to lay their eggs. Like most ‘blues’ the caterpillars have a honey gland which makes them attractive to ants which provide a measure of protection from some predators. They are, however, nowhere near as dependent on ants as the Large Blue. The caterpillars will develop and then pupate in July and the second-generation butterflies will emerge in August. The offspring of this second generation may, in favourable years, go on to produce a third generation which will emerge in late September. Otherwise the mature larvae will overwinter hidden amongst vegetation.
Photos Peter Bright John Ball
Brown Argus: This diminutive butterfly is, along with the small blue, our smallest butterfly. Newly emerged adults are a rich brown colour and the orange crescents of spots show up clearly. In females the orange spots reach the front of the forewing whereas, in males, they fade out little more than halfway to the front edge. Its resemblance to brown versions of the female common blue can cause confusion. However, it is distinctly smaller and has no hint of blue scales on the wings or body, and, for those with a photo, the underwing spot patterns are distinctly different. This butterfly is a warmth loving species active in sunshine and in warm sheltered sites. The first generation emerges in May and early June. After mating the females seek out suitable food plants on which to lay eggs. In the past common rockrose was the main food plant and was why the butterfly was confined to sites with this plant. However, recently the butterfly now also uses common stork’s bill and other close relatives like dove’s foot cranesbill. This change of food preference and the increased temperatures of global warming have resulted in this butterfly spreading northwards again and recolonising many habitats from which it had been excluded by loss of common rock rose. The eggs laid in June will produce caterpillars that pupate in July with the second generation emerging in August. It will be the caterpillars from this second generation which will overwinter as a more or less mature caterpillar. Emphasising that it is a ‘blue’ that happens not to be blue the caterpillars are attractive to ants just as with its close relative the common blue.
Photos Simon Reece Peter Bright