The Comma has a white marking on its underwings resembling a comma. The wings have a distinctive ragged edge, apparently a cryptic form as the butterfly resembles a fallen leaf. The caterpillars are also cryptic, resembling a bird dropping. In the U.K the larvae feed on hop, stinging nettle, elm, and blackcurrant; in other parts of its distribution (e.g., in Sweden) it also feeds on sallow and birch. The species survives the winter in the adult stage, and adults are of two forms. The form that overwinters before reproducing has dark undersides of the wings, whereas the form that develops directly to sexual maturation has lighter colured wing undersides. Both forms can arise from eggs laid by the same female, depending mainly on the photoperiods experienced by the larvae, but also with an influence of host plants, temperature and sex of individuals.
In the 19th century the British population of the Comma crashed, and by 1920 there were only two sightings. The cause for this decline is unknown, but from about 1930 the population recovered and it is now one of the more familiar butterflies in Southern England, and is also resident in Scotland and in North Wales.