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Last spring (Signs of Spring 3, March 15, 2018) I talked about the evolution of the Lepidoptera (butterflies and moths). Fossilized lepidopteran wing scales have been dated to over 200 million years of age! This is very significant because the flowering, nectar producing plants which make up most of our modern day lepidopteran food base did not evolve until some 50 million years later! What could those earliest lepidoptera have been eating? The logical answer to this question is actually on display in the early spring when several species of butterflies emerge weeks before the flowering of nectar-producing wild plants.
Mourning cloak butterflies (Nymphalis antiopa) over-winter as adults. They find cracks and crevices in tree bark and fold themselves into these narrow, protective spaces to spend the winter in hibernation. In the spring they emerge, often when there is still snow on the ground, and sustain themselves for several weeks during which they mate and lay eggs.
The emerging mourning cloaks vigorously contract their thoracic muscles to generate body heat. They also conspicuously and very uncharacteristically bask in the sunshine with their dark, colorful, dorsal wing surfaces (purple to maroon edged by an inner line of iridescent, blue spots and an outer border of yellow or creamy white) exposed to incoming sunlight. The venter (underside) of their wings is a dark, striated blackish-brown with a pale, gray border. Typically, the mourning cloak at rest folds its wings together so that only the drab, camouflaging coloration of the ventral wings is visible to potential predators.
These early spring mourning cloaks, quite possibly like those first lepidoptera 200 million years ago, drink sugar-rich tree sap that runs from wounds or woodpecker holes in trees. They are especially fond of oak trees and oak sap. The mourning cloaks are often seen walking head-first down tree trunks searching for oozes of sap. Adult mourning cloaks also eat rotting fruit and flower nectar during the summer and are especially fond of the flowers of knapweed and scabiosa (“pincushion flowers”). Mourning cloaks, like many butterflies, also swarm muddy puddles and even animal feces from which they gather not only moisture but also vital salts and nutrients.
Mourning cloaks mate shortly after emergence from hibernation. Males typically select a sunny perch from which they watch for females. There is a brief courtship, and then the fertilized female lays from 30 to 50 eggs in encircling clusters on the small branches of some selected host tree or shrub species. These eggs hatch into small, black caterpillars that have white speckles and a very dark, continuous dorsal line.
The caterpillars are voracious eaters and readily consume the leaves of the American elm, aspen, cottonwood, hackberry, paper birch, and several species of willow. The caterpillars grow rapidly and undergo four molts as they move through their larval instar stages toward their inactive pupal stage. The pupa is encased in a gray chrysalis which hangs from a thread attached to branches or some other type of overhanging structure. The metamorphosis into adults takes about 15 days.
The eggs laid in early spring will pupate and emerge as adults by early summer (June or July). These adults may enter warm-weather inactivity phases (“aestivation”) and then re-emerge as the summer begins to fade. They then feed very actively in order to build up fat reserves for their hibernation. An individual experiencing this type of life cycle pattern may live up to 10 months or more! This makes the mourning cloak one of the longest lived butterflies in nature! These June or July emerging adults, though, may also, depending on the climatological conditions or levels of habitat resources, skip the aestivation phase and proceed directly to mating and egg laying. This second brood of eggs, then, hatches into caterpillars which grow, pupate and metamorphose into adults by August or September. This second brood, then, feeds voraciously to prepare itself for the long winter hibernation. In the northern sections of the mourning cloak’s range one or two of these seasonal broods are common. In the southern sections of the range, however, up to three brood generations can be seen.
The North American and European distributions of the mourning cloak are both expanding into more and more northern regions. It is thought that these expansions are yet another observation of the biological consequences of human induced global warming.
Emerging along with the mourning cloaks are the comma butterflies (Polygonia spp.). The comma, like the mourning cloak, can overwinter as an adult and thus can quickly take advantage of warm spring afternoons to feed on the sugar-rich flow of tree sap or early flower nectars. This gives the comma a fast start on its spring reproduction. Commas are especially found in moist woods in which there is an abundance of nettles growing on the forest floor. Nettles, along with elm trees and hemp plants, are the primary plants on which the comma caterpillars develop.
The commas (also known as “angel wings”) are less distinctively marked than the mourning cloaks. Their orange and brown dorsal wing surfaces, though, stand out clearly against the browns and grays of the early spring vegetation. Like the mourning cloaks, the commas have very drab, very inconspicuously colored ventral wings surfaces. When they land and fold their wings, they seem to disappear from sight.
Commas, also like mourning cloaks, have summer and winter generations. The eggs laid by the over-wintering commas hatch into caterpillars that feed extensively on their nettle or elm host plants. The final instars of these caterpillar stages then pupate and form chrysalises from which a “summer generation” adult emerges. These summer commas are recognizable by the predominately black, dorsal surface of their hind wings. They feed widely on nectar, tree sap and rotting fruit and may, also like the mourning cloaks, spend the very hot months of the summer in inactive, aestivative states. They mate and lay their eggs again primarily on nettles and elms, and the caterpillars from these eggs will pupate and emerge as adults in the early fall.
These “winter generation” commas typically have hind wings that are predominately orange in color on their dorsal surfaces. These adults fatten up and then tuck themselves into tree bark spaces where they hibernate through the winter.
Another early spring butterfly here in Western Pennsylvania are the tiny (1 inch across) spring azures (Celastrina ladon). These stunningly beautiful butterflies have neon blue dorsal wing surfaces that seem to glow as they fly about. When they land, though, and close their wings, like the mourning cloak and the comma, the bright color (and to all appearances, the butterfly itself!) disappears as the pale white under-wing colorations blend into the surrounding, early spring browns and grays. The spring azure unlike the mourning cloak or comma, though, overwinters as a chrysalis and finishes its metamorphosis into an adult as the winter starts to warm into spring. The spring azure is primarily a nectar feeder that emerges a bit later than the mourning cloak or the comma, ideally timing its appearance with the earliest blooming spring wildflowers. If plants are not immediately abundant, though, it may get nourishment, like the mourning cloak, from mud puddles, leaves and even bird and mammal feces.
The early butterflies of spring! In many ways a recapitulation of how butterflies lived in their first 50 million years! Slurping up tree sap and nutrients from mud and fecal sources. Waiting for the flowers to come!