Often overlooked in our own back gardens, the holly blue moves in and out of sight, a reminder of how much of the natural world unfolds unnoticed at the edges of everyday life
A flicker of blue, and it’s gone.
No other butterfly plays tricks on the eye quite like a holly blue. One spring, standing in our back garden, I thought I was getting the warning flashes of a migraine. Those telltale zig-zags at the edge of my vision, the sort that make you blink hard and rub your eyes. But when I relaxed and stopped trying to focus, there they were: tiny blue wings dancing in and out of the holly.
Unlike the blue butterflies of open downland and grassland, the holly blue prefers shrubs and trees, especially hedges full of holly and ivy. They do pause on leaves – occasionally – but even when you are staring straight at them, they can seem to vanish. Once their bright upper wings close, sky blue becomes a silvered underside sprinkled with black-speckled spots.
But look carefully and you may spot a female. Her blue upper wings have a darker border than the male’s, but it’s a subtle difference and tricky to see.
Part of their charm is how cheek by jowl they live with us. You definitely don’t need to travel to a nature reserve to find one: they’re in our gardens, in the unkempt areas of churchyards and the rough edges of parks. In spring they lay eggs on holly flower buds, while their second generation, later in the year, prefers ivy.
But not every holly blue takes flight. Hidden among the leaves, its caterpillars may already have been claimed by a tiny parasitic wasp, Listrodromus nycthemerus.
This wasp lays a single egg inside the caterpillar, and its larva grows inside the caterpillar’s body until the moment a butterfly should appear. Instead, a wasp emerges. It’s one of the reasons holly blues can seem plentiful one year and scarce the next. Gruesome, perhaps, but it has been this way for thousands of years.
On a sunny afternoon, though, none of that is visible. There’s just a flicker of blue moving through the hedge, easy to miss unless you know what you’re looking for … and now you do.
by Jane Adams
