Satyrium w-album spend the majority of their lives in the tree tops, feeding on honeydew. 
  The dorsal wing sides are a dark brown with a small orange spot in the bottom corner of the hindwing. The male has a small pale spot on the forewing made up of scent scales.
   The ventral sides are a lighter brown with a thin white line, the "hairstreak", which gives this group of butterflies their name. On the hindwing this streak zigzags to form a letter W (or M) from which this species gets its name. The outer edge of the hindwing has an orange border, but there is no orange on the forewings as on the similar black hairstreak and there are two short tails, the female's longer than the male's on the hindwings.
   Part of a group known as "lateral baskers", they always rest with their wings closed, usually at right angles to the sun during day.
    Adults fly from late June until mid - of August in the UK, where there is one brood a year. They  occasionally fly down from the canopies to nectar from flowers when honeydew is unavailable, particularly after heavy rains have washed the honeydew from the leaves. The preferred flower observed in the UK is creeping thistle, but bramble and others are also used. In France, the butterfly has been found nectaring on Buddleja davidii, but the flowers of the lime tree appear to be its favorite.
   Eggs are laid singly, usually on the girdle scars near the terminal buds of elm trees. (Wych elm seems to be  preferred).
   They are a small butterfly with an erratic,
spiraling flight typical of the hairstreaks