2011-09-03 / Columnists

Nature Notes

Butterfly Metamorphosis: Caterpillar Crawling To Fluttering Flight
By Patricia Martin

What is it about butterflies that seems to fascinate us? Is it their ability to fly, their beautiful colors, their apparent delicacy, or their metamorphosis from one stage to another? In song, in poems, and in prayer, they’ve been used as symbols of freedom, joy, rebirth, and hope. One side of my brain appreciates all these images and beauty, the other part, perhaps the scientist in me, is more interested in the reality of these insects who share the warm summer months with us.

Butterflies and moths make up the insect order known as Lepidoptera, a major characteristic of which is that they have scales. Butterflies generally are daylight fliers. Unlike their cousins, the moths, they have thin, club-like antennae and they have the manner of holding their wings upright over the body when at rest.

Butterflies go through a complete metamorphosis. They begin with the egg, which hatches into a caterpillar, which will form a chrysalis, and then the adult butterfly. Most butterflies complete one or two generations in a summer season. Most adult butterflies live from only a few days to a couple of weeks, but some live much longer. On Mackinac, we have two species that live quite a long life, the monarch and the mourning cloak, both of which I’ve written about before. The monarch, which migrates to Mexico in the fall, may live eight months or more, and the mourning cloak, who winters with us up north as an adult living in rotting logs, can also live up to eight months. (These are the black butterflies with the yellow band along the edge of the wings that are usually the first butterflies to appear in the spring.)

In the United States and Canada, there are about 900 species of butterflies, and, in Michigan, 159 species have been recorded. Up to 137 of these could be considered a permanent resident of the state, the others are occasional visitors. One of the reasons for the numerous species of butterflies in Michigan is because of the diversity of habitats that can be found in this state. From hardwood forests to pine barrens, from swamps, marshes, and bogs to prairies and dunes, Michigan has lots of habitats in which different butterflies can thrive. Even so, 11 species of butterflies are on the endangered and threatened species list in Michigan, and 14 others are of special concern. This is primarily owing to habitat destruction by development and some farming practices.

White Admiral White Admiral Recently on Mackinac, several species of butterflies have been spied. Besides the monarch and the mourning cloak, painted ladies and the ubiquitous cabbage butterflies have been spotted. In addition, several of the admirals have been seen, and they’re not part of the U.S. Navy. These butterflies are part of the brushfoots, whose name comes from the fact that the males’ front leg are reduced to brush-like appendages.

The first is the red admiral (Vanessa atalanta rubria), whose upper surface of the wings are black with distinctive red bands and a few white spots toward the apex of the wings. The undersurface of the fore- wing is similar, but the hind wing is mottled and has no red band as seen from below. The adults of this butterfly live on the nectar of red clover, bog laurel, lilac, common milkweed, staghorn sumac teasel, and joepye weed among others. They also feed on tree sap and rotted fruit. The caterpillar is blackish to yellow green with yellow and black stripes and covered with black spines. The eggs are laid on nettles in Michigan.

These butterflies are found throughout Michigan near swamps, marshes, meadows, disturbed areas, and in gardens and parks, and have been seen in Michigan from April 23 to October 29. They are fairly common throughout the state and have two broods each year. It is not known how they winter over, as the adults cannot survive the cold, but they probably hibernate over in some form.

The second admiral that has been seen is the white admiral (Limenitis arthemis artemis). Like the red admiral, the upper surface of the wings are black, but instead of the red band, theirs is, logically enough, a white band. The hind wing has a submarginal row of orange spots. The undersurfaces are similar to the upper, except that the ground color is gray to orange gray with orange spots near the bases of the wings.

These adult butterflies are not usually found on flowers, with the exception of common milkweed and joe-pye weed. They usually take nutrients from damp soils, bird feces, and other organic matter. The eggs of this butterfly are laid on birch and aspens, though they may also be found on juneberry and haw- thorn. The caterpillars are a mottled brown or green with a whitish saddle patch and lateral line and clubbed horns. It is in the caterpillar stage that they winter over in a hibernaculum on the host plant.

White admirals are found throughout the Upper Peninsula and northern lower Michigan. They are common in northern forest openings, edges, trails, and along roadsides. Like the red admiral, they produce two broods and have been seen in Michigan from May 21 to September 20.

There is one related species that I would like to know if anyone has seen on the Island. It is the red-spotted purple (Limenitis arthemis astyanax). They’re black on the upper surface with purplish blue on the outer portion of the hind wing. Their undersurface is similar to the white admiral, except they lack the white band. They may also hybridize with the white admiral. These are found throughout lower Michigan in habitats similar to the white admiral.

During the next few weeks, keep a lookout for these and other butterflies before the cold weather comes and they disappear for the winter. Enjoy them for their flight, their beauty, their fragility, or their strength, their symbol of rebirth, freedom, hope, or whatever, but enjoy them while you have a chance.

Thoreau wrote: “See a little blue butterfly fluttering about on the dry brown leaves in a warm place by the swamp side, making a pleasant contrast.”

Trish Martin is a year-around resident of Mackinac Island, has earned a master’s degree in botany from Central Michigan University, and owns Bogan Lane Inn.

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