Holly blue is the other butterfly than could be confused with a common blue, however, its behaviour is very different. Holly blues tend to fly strongly around bushes and shrubs, often quite high up; by contract common blue fly low to the ground. The holly blue is also the first of the blue butterflies to be seen each year, emerging in March and April. For me the sighting of my first holly blue is as significant an event as hearing my first cuckoo a month or so later – it is a harbinger of spring.
Holly blue is an intriguing species. It was once a much more localised butterfly, but its range has expanded significantly in recent years and is now commonly seen in gardens, even in urban areas. The sight of holly blues flying around parks in Dublin is not uncommon, and delightful to see. But holly blue populations vary significantly from year to year, and years when they are very plentiful can be followed by years when they are very scarce. It is thought that this population cycle is due to predation of holly blue by ichneumon wasps. Predation rates by ichneumon wasps increase as the butterfly population increases, only for the butterfly populations to crash when predation levels reach a certain level.
Here in Bramblestown, holly blue is most often seen in April and May, and again in August in years when it has a successful second brood. I find this a difficult butterfly to observe at close quarters, as it is always actively flying. But, as luck would have it, early one morning I noticed one on our garden hedge, and it remain still long enough for me to get my photograph. Job done!
Speckled wood #1, Dingy skipper #2, Wall brown #3, Common blue #4 & Holly blue #5.