Blue

Holly Blue (Celastrina argiolus)

For years now, I've been trying to get a picture of this little butterfly: the Holly Blue (Celastrina argiolus). The problem is that it almost never, EVER alights! Instead, it flits around the garden, touching down (if at all) for only the briefest of moments. About the time the camera focuses, the butterfly is off again. But last week, I got lucky. This female returned again and again to a bush just outside the house, presumably checking it out as a potential site to lay its eggs. The butterfly gets its name from the primary host of its spring larvae. That first generation feeds principally on the buds, berries and terminal leaves of the Holly tree while a second generation, which emerges later in the summer, is found primarily on Ivy. In both generations, larvae will also feed on various other shrubs and vines, including spindles, brambles, dogwoods, snowberries and gorses. Our garden has both Holly and Ivy, plus plenty of brambles, so I'm sure this little female can find somewhere appropriate to lay.

The Holly Blue is one of two blue species we get here. The other, Common Blue, is distinguished by orange spotting on the underwing. Adult Holly Blues emerge earlier in the spring – as early as April, as opposed to June for the Common Blue. According to the Butterfly Conservation's website, the Holly Blue tends to fly higher than other blues, which typically stick close to the ground; maybe that's why I don't seem to see as many of them. They also go through big population swings from year to year, primarily because they're regularly attacked by a parasitoid ichneumon wasp, which lays its eggs in the butterfly's developing caterpillars. The caterpillars serve as the only host for the wasp, so when their numbers inevitably collapse, so does the wasp's population. This allows the butterflies to recover, with the wasp numbers slowly following. And so the cycle continues! The butterfly is common and widespread in England and Wales, and rarer in Scotland and northern Ireland, though it is spreading steadily northwards. Elsewhere, it is common across much of Eurasia – and serves as the national butterfly of Finland.