Holly Blue
As the name suggests, the caterpillars of this butterfly feed on holly. In fact, only the spring brood feed on holly; the summer brood feed on ivy. So it could just as easily have been called the Ivy Blue. This is the largest of Ireland's three Blue butterflies. Females (seen here) have black edges to the upper forewings. Males are pure blue.
National Parks & Wildlife Service, 7 Ely Place, Dublin
2. Phone: +353 1 8882000 Fax: +353 1 8883272