It’s not often that the reserve’s first reported butterfly of the year is a comma. This pair, basking in the sunshine, were photographed by Clive Knight on Monday.
The comma (Polygonia c-album) overwinters in woodland, disguised as a dead leaf by its ragged outline and the cryptic colouration of its underwing. After emerging from hibernation, both male and female search out early nectar sources, such as pussy willow or blackthorn blossom. The males stake out territories while the females range more widely.
Once mated, the female lays her eggs on the fast-growing spring stinging nettles. This first brood of caterpillars, well camouflaged as bird droppings among the nettles, grow, pupate and emerge as adults in June and early July. Some of this mid-summer generation of adults have dark underwings and go on to hibernate through the winter. But some are more brightly coloured with quite light underwings; this form mates and produces another late-summer generation that then overwinter.
Comma caterpillar (larva) and adult (imago) on stinging nettles. The white comma mark, for which the species is named, is quite clear on the butterfly’s underwing.
Apparently, if day length is increasing (before midsummer’s day) as the caterpillars develop, then the majority of adults will be the light form that go on to produce another brood, but if day length is decreasing, then the majority of the adults will be the regular dark form that enters hibernation.
The comma population has increased steadily since the 1960s, recovering from a sharp and dramatic fall in the 19th century that was associated with the reduction in hop farming, an important larval foodplant at the time. The species has evolved from the few that laid their eggs on nettles, a very successful strategy that will always find food for their caterpillars somewhere and will never put the species in competition with our farmers.