The chalkhill blue is a small butterfly that loves the horseshoe vetch plant. They're found only on chalk and limestone downlands, making the Commons the perfect habitat for them.
Despite its size, this pretty little butterfly more than makes up for it in colour. The males have unmissable milky blue wings that have a deep dark brown border, fringed with white. The females are much duller and spend less time flying.
From August to October the butterfly can be seen laying its eggs on the stems of the horseshoe vetch. The eggs eventually fall to ground where they spend the winter, hatching only when the ground warms in spring.
The caterpillar feeds on the leaves of the horseshoe vetch. The chrysalis is then taken by the ants on the common and buried underground. It remains buried for about four weeks when it emerges as a butterfly in July.
The weather over the last ten years has not been so kind to the chalkhill blue, causing a sharp decline in its distribution nationally. It's now classed as a butterfly of conservation concern. It's found only from a line running south east from west Gloucestershire to Cambridgeshire.