Chalkhill Blue vs Common Blue

The male Chalkhill Blue has pale silvery-blue upper wings with thin dark edges, while the females are chocolate brown with orange spots around the edges. The undersides of the wings in both males and females show a pattern of white spots with black centres and orange crescent shapes on a grey-brown background. This butterfly is larger than many similar blue butterflies, with a wingspan of up to 40 millimetres. It is found only in chalky grasslands in southern England, especially on chalk downs and limestone hills from Dorset to Kent. The colonies are very localised and depend closely on their caterpillars’ food plant, horseshoe vetch. Adults appear from late July to early September and have just one generation each year. Males gather openly on bare ground and on flowers, particularly knapweeds and scabious. The species has a special relationship with red ants, which look after the caterpillars and pupae. In return, the ants receive sugary secretions from the larvae.

The Common Blue is the most common blue butterfly in Britain, but males and females look very different. Males have bright violet-blue upper wings with a thin white edge, while females are mostly brown with orange spots along the edge of their wings and often have some blue scales near their bodies. Both males and females have orange spots and pale blue areas on the underside of their wings. This butterfly lives in places with lots of flowers, such as grasslands, coastal sand dunes, heathlands, and roadsides all over the British Isles. It can be found wherever the plants its caterpillars eat are growing. The caterpillars feed only on plants from the pea family, especially Bird's-foot Trefoil and Common Restharrow. The adult butterflies appear in two or sometimes three groups of broods between May and September. Males usually come out a little earlier than females. They are often seen feeding on nectar from low-growing flowers or resting with their wings open on bare ground when the sun is shining.