Monarchs-to-be zero in on lunch > Caterpillars proceed to feed on butterfly weed and its kin

Last week in “Trellis and Trowel,” I spent the first part of the column lamenting the fact that I haven’t seen many bees and butterflies this year. Well, it seems I spoke — or wrote — too soon.

Two days after writing the column I took a walk through our cutting garden only to find the butterfly weed absolutely covered with larvae of the monarch butterfly. They may have been there before, and I may have not noticed them, their light-green coloring masking their whereabouts. But that day I couldn’t miss them. They had fed so heavily on the plants that only a few petioles and leaves remained.

We counted 122 — 122 caterpillars on 18 plants.

Over the next 24 hours, the caterpillars completely defoliated the plants. Where bright-orange flowers of the butterfly weed, Asclepias tuberosa, had been gloriously displayed a couple of days before, only stout stems remained. To the left of the butterfly weed the ageratum stood tall and proud. To the right, the larkspur remained unscathed. But the poor butterfly weed took the hit hard. Soon the bare stalks will be brown and lifeless.

Last week I wrote to give a pitch for butterfly gardening, and although I’m happy to sacrifice a few plants in the name of perpetuating the monarch species, in the past when I’ve thought about butterfly gardening, I’ve thought only of attracting butterflies for their beauty and function — a very one-sided view.

The events of the past week have shown clearly that butterflies, too, have a one-sided view of things: My garden is food. I planted the butterfly weed for its pretty flowers and expected to see lovely butterflies fluttering from bloom to bloom. I forgot that to become a butterfly a monarch first must be a caterpillar. And a mighty hungry one, at that.

I called Ron Mack, Maine state pest survey coordinator for the University of Maine Cooperative Extension, to get the lowdown on the status of monarchs in Maine this year. According to Mack, the adults seem to be common within the state right now. He said that in past years there has been a noticeable decline, but all looks well for the insects so far in ’97.

“Adults have been nectaring and laying over the past few weeks,” Mack said. “The caterpillars feed on milkweed and related plants.”

According to Mack, some monarchs spend the late summer months in Maine, while others summer across the country. Those that summer in our state overwinter in Florida.

“Monarchs have a couple of overwintering spots, actually,” Mack said. “The most famous one is down in the mountains of Mexico. Most of the specimens that overwinter there are from the western and middle parts of this country. I understand that millions and millions are in the trees at once.”

Mack reported that a couple of years ago the monarchs had a hard time overwintering, and the migration north was negatively affected.

The annual migration is quite a trek for the butterflies.

During the migration north, adult butterflies will stop to lay eggs. The larvae feed, metamorphose and eventually become adults that fly farther north.

“They’ll have a generation in, say, Georgia, then those adults will fly north to, say, Virginia. By the time they get to Maine they are a couple of generations removed [from the original parent].”

Asked what affects the rate of northward progression, Mack said, “It has a lot to do with the life span of the adult and the biological pressures on the adult.” Thus, if butterflies continually encounter gardens and fields with fodder and shelter, their northward progression may be hastened.

According to Mack, our short summer provides a relatively small window of time in which to enjoy these colorful insects. Monarchs, he said are “univoltine, producing a single generation per year. In a longer-season climate these insects are able to produce many more generations.”

The monarch is the flagship species of butterflies, according to Mack. “It tends to fly later in the season. There are several other species, though. The tiger swallowtail is the big yellow and black butterfly you see in June and July. They feed on aspen, cherry and other plants. The black swallowtail is another species. The larvae feed on members of the carrot family. That includes dill, carrot, wild Queen Anne’s lace, parsley, fennel.”

Mack noted that one interesting point about the black swallowtail caterpillar is that if you pick it up and give it a gentle squeeze, its osmaterium, a foul-smelling gland located behind the head capsule, will emerge. This is the larvae’s defense against predators.

I have no particular attachment to butterfly weed, so this whole experience with the monarchs has been far from unpleasant. Had they taken a liking to my lady’s mantle or hollyhock, I’d have been upset. In fact, this has opened my eyes to the needs of butterflies as components of the environment, where before I viewed them mainly as ornaments. Next year I plan to plant some butterfly weed away from the garden to give the butterflies a little more of a peaceful haven.

There will be a garden celebration on the evening of the full moon, at 6:30 p.m. Tuesday, Aug. 19, in the moon garden at the Penobscot County Master Gardener Demonstration Garden at Rogers Farm on the Bennoch Road in Stillwater. Maine poet June Tucci will be the guest of honor and there will be live entertainment by local musicians. The event is free and no pre-registration is required. Refreshments will be served and, in the event of rain, shelter will be provided. Rogers Farm is on the Bennoch Road between Stillwater and Route 43. For information, call the Extension Service office at 942-7396 or 1-800-287-1485.

Diana George Chapin is the NEWS garden columnist. Send horticulture questions to Gardening Questions, c/o Maine Weekend, Bangor Daily News, P.O. Box 1329, Bangor 04402-1329. Selected questions will be answered in future columns. Include name, address and telephone number.