by Roy Lukes

Hardy Butterflies, Larvae Prepare For Winter


Tomato Hornworm

What a great summer it has been at our place for gardening. Only the carrots are still in the ground, ready to be dug and stored for the winter. Our friend, Carl, delivered several large loads of goat and sheep manure for the past two falls that was tilled into the soil before it froze. That "gardeners’ gold," combined with plenty of rain and warmer than usual air temperatures undoubtedly did the trick.

The sweet corn was awesome in quantity and quality, and the tomatoes were never better. Along with the tomatoes also came a small number of tomato hornworms (actually caterpillars!) which I never kill. They are gently lifted off the plants and placed well outside the garden fence. I happen to be very fond of hawkmoths, and the tomato hornworm is the larva of the five-spotted hawk moth whose wings are around four and one-half inches across. Orange-yellow spots decorate the sides of its abdomen.

The white diagonal stripes form "V" angles around the spiracles, appearing like small portholes on both sides of the caterpillars. These small circular openings allow the passage of air in and out of the larva’s body. What appears like a sharp barb or thorn on the posterior of the caterpillar is quite harmless, even to the touch. Whereas I have never seen one of these caterpillars work itself into the ground, I’ve heard that the stiff rear horn helps it accomplish this important task.

Once below the surface of the ground the larvae pupates, forming a hard brown case that appears as though it had been varnished. Look closely and you will see that it even has a tongue case, resembling a jug handle, near the head. The pupa will overwinter underground.

Even though we have never made actual counts, it appears as though the number of woolly bear caterpillars crossing roads this early fall is as high as we’ve ever seen. My guess is that more people know this caterpillar than any other. What they may not know is that they will spend the winter in this form, continue eating next spring, finally pupate and emerge as an Isabella moth. This moth has a wingspan of around two inches. The slender forewings are a rich tan while the rear wings are light yellow. Females are darker than the males.

Carefully touch the hairs of this larva and you’ll find that they are not soft and woolly but rather stiff and bristly. Color variations of the reddish-brown and black bands don’t predict the severity of the approaching winter. Rather they reflect the caterpillar’s age and other variable factors. Young caterpillars, for example, will have narrower brown bands than the older ones.

At least four well-known species of butterflies from this region also spend the winter in the larval or caterpillar stage, the northern pearly eye, great-spangled fritillary, viceroy and white admiral. What never ceases to amaze me is that once the eggs of the great-spangled fritillary hatch those extremely tiny larvae eat one meal of grass leaves, then head down into the duff lying upon the forest floor. There they will remain, having had only one meal, until next spring when they will resume their eating.

Quite a few of the butterflies that are recognized by many people will be spending the winter months in the chrysalis stage. Included are the spring azure, black swallowtail, tiger swallowtail, cabbage (white), and the common sulphur.

For some unknown reasons the large so-called silk moths of our area were considerably down in number compared to previous years. These sharp dips in population are known to periodically occur with many other moth and butterfly species. All of the four silk moths overwinter in the cocoon stage. They are the cecropia, luna, promethea and polyphemus.

And now one comes to that wonder of wonders, those "frail" butterflies of this region that are capable of spending the long cold winter as adults. Unlike the popular monarch butterflies that, like miniature "snowbirds," spend the winter south of the border, eight of our hardy species crawl behind a piece of loose bark on a tree, or squeeze their way into a woodpile, and stay put.

Included in this unusually rugged group are the mourning cloak, Milbert’s tortoise-shell, Compton’s tortoise-shell, question mark, comma (hop merchant), red admiral, painted lady and the painted beauty (American painted lady).

Regardless of the stage in which moths and butterflies spend the winter at this latitude, they aren’t as frail as we think they are!

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This column appeared in the Door County Advocate on 10/29/1999.
© Copyright 1999 Roy Lukes. All rights reserved.