The sight of butterflies in early spring, near my home in Mississauga, raises a couple of interesting questions: first of all, where did they come from? Butterflies have to start out life as caterpillars (once they emerge from the egg, that is), and caterpillars have to have something to eat. The supply of caterpillar-friendly plants during a Canadian winter is understandably on the low side. Secondly, if there aren't a lot of spring flowers readily available, where do the adult butterflies get their food?
Here is a butterfly that provides answers to both questions: the Mourning Cloak (Nymphalis antiopa). The adults live for 10 or 11 months, and can be seen flying about even as the last snows are melting at the end of winter. These early spring butterflies actually emerged in the previous August, and have survived the winter by overwintering in the adult stage. Their parents were, and their offspring will be, probably part of a shorter-lived summer brood that flies in June or July – a pattern called bivoltine. In other parts of its wide range, though, the Mourning Cloak is univoltine, with only one brood per year.
Mourning Cloaks that fly before, or after, flowers are available get their food from tree sap. On May 12, 2012, that is what Eileen and I found numbers of them doing along the banks of the Credit River in Erindale Park, Mississauga, a short distance from our home.
Mourning Cloaks may appear rather sombre creatures - hence the name, I suppose - but when the sunlight hits their wings they take on a rich burgundy glow. In Britain, where it is a rare and much-valued visitor from the continent, the Mourning Cloak is known as the Camberwell Beauty - altogether, perhaps, a more deserving name.
I remember meeting some British birders at Point Pelee, Ontario, and sending them into a frenzy of excitement by by pointing out a Mourning Cloak/Camberwell Beauty - a commonplace to us, but a stunning rarity for them.
The Mourning Cloak is not the only sap-feeding butterfly. Red Admirals (Vanessa atalanta), frequently elbowed their way to the table, sometimes even landing on the larger butterflies.
The Red Admiral has a different strategy for surviving the Canadian winter: migration to a warmer climate, in this case the southern United States (in mild winters some do overwinter here), where they breed and die. The butterflies that return the following spring are their offspring.
The Eastern Comma (Polygonia comma), a cousin of both the Mourning cloak and the Red Admiral, has an intermediate strategy: it will hibernate over the winter (or at least the second brood of the year will -this is another bivoltine species), but it may migrate some distance to the south first. It, too, is often a sap-eater.
Juvenal's Duskywing (Erynnis juvenalis) is one of the skippers (Hesperidae). It overwinters, unlike the nymphalid butterflies we have seen so far, as a caterpillar (having, presumably, fattened up first), emerging as an adult in early May. In the south of its range, in northern Florida, adults may appear as early as January.