Butterflies are common; a notable example is the Chalkhill Blue, which is particularly well suited to uncultivated chalk downland areas.
The downs are home to a wide variety of wildlife including many rare wild flowers, such as the Bee Orchid, and different butterfly species, like the Marbled White and the Chalkhill Blue.
Up to 32 species of butterfly have been recorded on the downs including the Adonis Blue (Lysandra bellargus), Chalkhill Blue (Polyommatus coridon) and Small Blue (Cupido minimus).
After the park was formed, these grasslands were cleared of scrub to allow the rare chalk land plants and animals to re-establish including the Musk Orchid, and Chalkhill Blue butterfly.
The principal arguments of the protesters were their concern about making wildlife species, such as the Chalkhill Blue butterfly, extinct, putting a highly visible scar on the landscape, and that they believed the new motorway would not adequately resolve traffic problems.
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Butterflies include chalkhill blue, Brown Argus and silver-spotted skipper; the latter was re-introduced to the site in 1998.