Wildlife Watch: Adonis Blue

For June I'm looking at the Adonis Blue butterfly, so named after its beautiful bright blue wings. This is a butterfly that's found on warm dry calcareous grassland (chalk or limestone) and as such it is restricted to the south of England in the UK. In the past numbers have declined rapidly thanks to the intensification of farming but it has since seen some recent recovery. It's also the symbol of the Kent Wildlife Trust.

Adult males have bright sapphire wings on their uppersides and can be distinguished from other blue butterflies by this as well as the presence of dark lines that cross into the wings' white borders. This 'checkering' is also present on the female Adonis blue but she has dark chocolate-coloured wings instead with some orange spots along the edge. This is very similar to another butterfly, the female Chalkhill blue but the Adonis blue female can be distinguished by the presence of blue scales by the orange spots on the hindwing which are white in the Chalkhill. On the underside, like most blue butterflies, the wings are a warm grey/brown with black spots ringed in white with rows of orange spots near the wing edge.

(Left) Female Adonis blue                 (Right) Side view of a male on marjoram

This butterfly needs a short sward (grass height) of ideally 1-4cm to flourish. This is because it creates a warm microclimate for caterpillars to develop. Caterpillars are green and hairy with two central yellow broken lines running down their back and two thin yellow lateral stripes. They have only one food plant - Horseshoe vetch.

Caterpillar on Horseshoe vetch

Adults feed on nectar from flowers such as wild marjoram and ragwort, and males may also be found in groups on animal dung extracting nutrients. As such it needs a diverse grassland habitat that is grazed at least some of the year and favours south-facing slopes.

There are two generations every year with the first emerging around May and a second in August. They are roughly on the wing for a month where they mate and lay eggs, singly, on horseshoe vetch. Like other blue butterflies the Adonis blue has an interesting symbiotic relationship with ants. Caterpillars produce a sweet secretion from a gland which ants are fond of. In return the ants will protect the caterpillars and later the pupae from predation, even creching them together and burying them at night in a small underground cell to protect them. After overwintering as a caterpillar, often in ants' nests the Adonis blue will be ready for metamorphosis the following year.