The White-letter Hairstreak is a small butterfly with an erratic, spiralling flight typical of the hairstreaks.  It is distinguished by a strongly-defined white 'W' mark across the undersides.  The dark uppersides are seen only in flight as the butterflies always settle with their wings closed.  Adults are difficult to see because they spend so much time in the tree canopy, although they occasionally come to ground level to nectar on flowers near elm trees or scrub saplings.  The species declined during the 1970s when its foodplants were reduced by Dutch Elm Disease, but it seems now to be recovering in some areas.