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Holly blues thrive in parks, gardens and churchyards where the holly and ivy they require for egg laying are in abundant supply. As a result their range has spread and there are now 46% more in Wales than there were in the 1970s.

Their blue wings are edged with a black border on the upper side, and the pale blue underside is sparsely speckled with black spots.

Holly blues are found in the countryside along hedgerows, field margins and woodland rides, as well as in gardens and parks.

The common blue butterfly is similar in appearance, but has pale brown underwings with lots of black and orange dots fringed with white.

The holly blue is the more likely garden visitor, and will fly much higher around bushes and trees. The common blue is mainly seen fluttering over flower-rich grasslands.

A parasitic wasp called Listrodomus nycthemerus will only lay its eggs in holly blue caterpillars. As a result, the holly blue numbers fluctuate on a cyclical basis according to the abundance of parasites.