The map butterfly (Araschnia levana) is a fascinating butterfly that produces two entirely different-looking forms. This phenomenon, known as seasonal dimorphism, means that its development varies depending on the time of year. The length of the day during the caterpillar stage determines the butterfly's color form. Caterpillars growing under long-day conditions (15 to 17 hours of daylight) develop into the summer form without a dormant phase. Conversely, if the caterpillars grow during shorter days, they enter a state known as diapause and, after overwintering, develop into the spring form.
[Summer form (top) and spring form (bottom). Photomontage: Reto Künzler]
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