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NATURE HAPPENINGS - March 2006


Mourning Cloaks in the Morning
by Damian Fagan

The weather shouts “March!” as last week’s snowstorm melts into the warmth of today. Spring has sprung, as red-winged blackbirds sing, cottonwood buds seem ready to burst, and the first butterflies of spring, the mourning cloaks, bask in the morning sunshine.

Gathering warmth through their dark wings, these butterflies are named after the traditional woolen cloaks or coats worn back in the 1800s while someone was “in mourning”. In Europe and Eurasia, where this species also occurs, these butterflies are known as Camberwell Beauty, after their initial discovery in 1748 near Camberwell, London. For when the light strikes their purplish-black wings, they are indeed beautiful creatures.

A thick yellow to tannish band borders the margin of the wings and is visible when the wings are folded open. Inside of this border is a row of iridescent blue spots. These spots are barely visible when the butterfly folds its wing up, and the irregularly scalloped margin helps the butterfly blend into its surroundings. Camouflaged against a tree trunk or the ground, these medium-sized butterflies may be overlooked.

But in the spring, they stand out when in flight because they are the only butterflies about. These early season adults are those that overwintered, hiding beneath a flake of bark or a rotting log or perhaps some loose siding. Depending upon their location, as these butterflies occur throughout North America except for the Gulf States and Florida, these adults seek mates before they die.

Instead of flying all about, the males tend to sit and wait for receptive females to fly into their territory. After courtship, the females lay numerous eggs (20-50) in loose groups on host plants that include willows, elms, hackberries, cottonwoods, aspens, and birches. The eggs hatch in concert with the spring leaves, thus ensuring an ample food supply for the caterpillars. Often a swarm of caterpillars will be encountered.

The caterpillars tend to congregate on plants until they are much older and start dropping from the trees and dispersing. Then the caterpillars might be observed singly or in small groups. The caterpillars are easy to identity as their dark bodies have numerous bottlebrush-like hairs projecting from reddish bases. The coloration and presence of the hairs is to deter predators – mostly birds – from consuming the individuals.

The young caterpillars go through several growth stages and shed their skin with each stage. In late spring the caterpillar will spin a short section of silk that enables them to hang downwards from a limb or protective overhang. Looking like an inverted J, the caterpillar enters into its final adolescent stage, the chrysalis, where it turns into the proverbial beautiful butterfly.

This metamorphoses period takes about two weeks, but not all of the grayish chrysalises mature. Those adults that do survive emerge from their pupas and find a safe location to dry their wings. Sometimes afterwards, which might be weeks away, the adult will enter into a temporary hibernation called aestivation. Afterwards the adults will emerge and feed prior to winter.

Though the butterflies feed mainly on tree sap, you can place a plate of rotting bananas, melons or peaches out to attract adults to your yard. Though these butterflies will drink nectar from flowers, this behavior is the oddity, not the norm. Sometimes you might encounter one of these adults walking head downward along a tree trunk searching for a wound or woodpecker hole from which sap is flowing.

So if you encounter one of these long-lived butterflies, give them a break. They have endured the tests of winter only to begin the trials of spring - a condition that led to their official designation as the Montana State Butterfly in 2001.

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