Look Out For: Comma Butterflies

Comma underwing

At last, butterflies are starting to emerge in numbers after the winter and, on a fine April day, you stand a good chance of spotting a Comma butterfly.

Commas, named from the comma-shaped silvery mark on the underside of their hindwing, are similar in size to the familiar Small Tortoiseshell and also have a similar reddish-orange appearance in flight. When perched to bask or drink nectar, however, the distinctive deeply-scalloped (sometimes referred to as “ragged”) wings of the Comma immediately distinguish it from any other UK butterfly.

Comma (Tim Melling)The Commas being reported now, in good numbers according to many observers over recent weeks, have spent the winter as dormant adult butterflies, and are emerging now to breed. Unusually for butterflies, these overwintered adults are a mixture of the offspring and grand-offspring of the Commas that flew last spring. This arises because Comma caterpillars developing in the late spring and early summer can take one of two developmental pathways. Either they develop into a hibernating adult butterfly, which will simply feed up in summer and then enter its dormant overwintering state, or into reproductive adults that will breed and die during the summer (and whose offspring will develop rapidly during late summer and autumn and then hibernate as adult butterflies).

The proportion of Comma caterpillars taking each route varies from year to year depending on the weather. In warm years, when the caterpillars grow more quickly, more develop into the reproductive adults and, in effect, fit an extra generation into the year. In cooler springs, a greater proportion of caterpillars develop into hibernating adults, effectively playing it safe by not trying to fit in an extra brood during a year when the chances of success are reduced by the weather.

Comma hutchinsoni (Tim Melling)Not only is this a clever adaptation to deal with the vagaries of the weather, but you can see it in action with your own eyes. The two different sorts of summer Commas look subtly different; the reproductive ones are a form named hutchinsoni and have brighter golden-orange upperwings and paler brown colours on the underside of their wings compared to the adults that are destined for hibernation.

The Comma is one of the minority of UK butterflies that has fared well over the past few decades. Confined to southern parts of Britain for much of the twentieth century, it has spread northwards rapidly, colonising northern England and swathes of southern and central Scotland, as well as colonising the Isle of Man and south-east Ireland.

Richard Fox

Head of Recording

Follow me on Twitter: @RichardFoxBC