Commas' seasonal colour schemes

 

Comma butterflies Polygonia c-album produce two generations per year, each with its own colours, shape and markings. When overwintering adults emerge in spring the females lay eggs on stinging nettles, where the caterpillars feed and after pupation emerge in early summer looking like this female, with orange-brown wings bearing rather pale marking. They lay eggs on nettles, where their caterpillars will be feeding now, and when they pupate and hatch the next generation of adults, emerging in late summer, will include many individuals that look like ….

 

…. this, with much richer red-brown background colour, darker and more well-defined markings and a brown border around the wing edges, emphasising the dead-leaf cryptic colouration This one was photographed last autumn, feeding on fallen pears in the garden; most of the commas that overwinter look like this.

Why the difference? I’ve seen speculation that it may the consequence of differences in the seasonal quality of the caterpillars’ diet and that daylength during the caterpillars; feeding period - lengthening in the spring generation, shortening in the summer/autumn generation - may have an influence.