The holly blue is a tiny butterfly, that can be seen throughout almost the entire northern hemisphere. It is a frequent visitor to gardens and parks where holly and ivy grow. Adults feed on the nectar from flowers of these two plants, but also on oozing sap, aphid honeydew and carrion juices.
The holly blue has a wingspan of only 26-35 mm. The upper side of the wings of both sexes is blue, although the females are slightly paler in color than the males. The forewings of the female have blackish borders that are absent in the male. The underside of the wings is a paler blue with distinctive black flecks. The holly blue has a pale blue body covered with hairs, long black antennae with white stripes along their length and pale blue legs ringed with black stripes.