The Comma (Polygonia c-album) is a species of butterfly, common in the United Kingdom and with a distribution across Europe and temperate Asia to Japan and south to Morocco. Similar species are found in the United States and Canada. It 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 19th century the British population of comma butterflies crashed, and by 1920 there were only two sightings. The cause for this decline is unknown, and from about 1930 the population recovered and it is now one of the more familiar butterflies in Southern England, and is now resident in Scotland and in North Wales.
The caterpillars will feed up on hops, and they will also eat stinging nettle, elm or currant leaves, and in other parts of its distribution (e.g. in Sweden) also sallow and birch leaves.
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.