It’s hard to mourn when the snow is is nearly gone, the pussy willows are emerging, and a Mourning Cloak butterfly flits across one’s path. Mourning Cloaks are among the longest-lived butterflies, with a lifespan of nearly a year. In the fall, Mourning Cloaks replace some of the water in their body with antifreeze-like glycols, which allow them to hibernate overwinter. Thus when the temperature rises in the spring, they are among the earliest butterflies to appear, surviving on tree sap rather than flower nectar.