The Holly Blue is a butterfly which goes through a cycle of being very numerous, then plummeting to low levels, then increasing again. This is thought to be due to a parasitic wasp by the name of Listrodomus nycthemerus, which kills the butterfly in its caterpillar stage – when the butterfly numbers have been reduced far enough, the wasp has no host on which to predate, so the wasp’s numbers reduce, allowing the butterfly’s numbers to increase, and vice versa.
Looking at the reports of Holly Blue to the website this April, it seems to be doing well, especially in Winterborne Stickland, where 17 were spotted at once, so we hope they are on the increase.
The Holly Blue is the only blue butterfly which flies this early in the year. Later on in the year, it is best identified by seeing its underside, which is pale blue with black spots. It has two broods during the year: in the spring, it lays its eggs on holly buds, and in the later brood, it uses ivy, though occasionally other food plants may be used by the caterpillar.