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The first dog face butterfly of the morning scudded by as Ron Panzer was introducing us to Gensburg-Markham Prairie. Two inches across, bright yellow marked with heavy black at the wing tips, the dog face soared and swooped, dancing in the sun. Later, Panzer caught one in his long-handled net and showed us the details of the wing pattern that give the insect its common name. The scalloped edges of the black at the wing tips outlined the profile of a poodle's head in the yellow of each wing. A black "eyespot" within the yellow added to the illusion.

Last Saturday, Gensburg was filled with dog faces, and by the end of an hour's walk, all nine of Panzer's students could identify a passing dog face. The mystery of the world of butterflies had been slightly reduced.

We nine students are all volunteer butterfly monitors recruited by the Nature Conservancy to keep track of wild lepidopterans on nature preserves in Illinois. Most of us will be working in natural areas in the forest-preserve systems of the six counties of metropolitan Chicago. So far as we know, we are the only volunteer butterfly monitors in the U.S., a position of leadership that is just what one might expect from this area.

Butterfly monitoring is a beginning, a first step into the realm of the invertebrates, the animals that hold the living world together. We vertebrates like to think of ourselves as the earth's dominant creatures. We are big, beautiful, noble, stately, and filled with dignity, But we are like Louis XIV and his courtiers. We stand around admiring each other's finery while the invertebrates, the peasants of the animal world, do all the work. Bald eagles may inspire our awe, but they are less important than bumblebees to the functioning of ecosystems.

Invertebrates pollinate almost all the flowers, aerate and fertilize the soil, and break down dead plant and animal matter, releasing minerals for another cycle through the system. They far outnumber vertebrates in numbers of species, in biomass, and in energy consumption. A study of a ten-acre piece of Maryland forest discovered 73 nests of a single mound-building ant species. The total population of workers was estimated to be 12 million. At an average weight of about 11.5 milligrams, those 12 million workers represent a biomass of about 300 pounds. These numbers account for only one of several species of ants in the woods, and ants represent only a tiny fraction of the total population of invertebrates.

In addition to their need for pollinators, many plants have other kinds of symbiotic relationships with invertebrates. A local prairie ant, Formica montana, carries the seeds of various native plants into its nests. The seeds are coated with ant candy, a substance the ants enjoy eating. The ants eat the candy, keep the seeds underground for a time--perhaps until they are ready to germinate--and then carry them back to the surface.

Invertebrates, especially insects, are a major source of food for creatures with backbones. We would have few songbirds without insects. Even seed-eating species often feed their developing young on a high-protein insect diet.

Nature preserves are supposed to be high-quality examples of native biotic communities, and they can't be that without healthy, diverse, and abundant populations of animals without backbones. Surveying all the tens of thousands of species of insects, spiders, nematodes, annelids, and centipedes is way beyond our resources. Surveying butterflies is a place to start, a way to begin checking the health of our preserves. Butterflies are relatively conspicuous and easy to identify. They occur in a manageable number of species--about 100 in the northern part of Illinois--and they are annuals, short-lived creatures whose numbers respond very quickly to changes in the environment. If something is going wrong, the butterflies will let us know right away.

Ron Panzer is the logical person to teach us how to survey butterflies. He is the site manager of Gensburg--the land is owned by Northeastern Illinois University--and he supplements that job with contract surveys of insect life for various conservation agencies. He is also a patient and enthusiastic instructor, the sort of person who makes the daunting task of learning all the local lepidopterans seem manageable, even easy.

We began our formal instruction in the small gravel parking area at the edge of the Gensburg prairie. Panzer showed us the chief article of equipment we would need, a heavy-duty net mounted on a long wooden handle. He also recommended some guidebooks to help us and showed us a few cases of mounted specimens.

The specimens raised some questions, the principal question being, should we take any ourselves? We may be dealing with very rare animals, and none of us wants to have our activities make them any rarer. Panzer tells us that we may have to take a few individuals of species that are very difficult to identify, but we should keep our collecting to a minimum. For most species, it will be enough to net them, examine them carefully, and release them--and we should be striving to develop our eyes to the point where we can identify the local butterflies on the wing without disturbing them in any way.

Panzer has got to that point himself. Like a skilled birder, he has assimilated all the details of shape, size, color, and behavior that make each species distinctive. He has assimilated all this so thoroughly that sometimes when we ask him how he knows that a particular fluttering insect is, for example, a wood nymph, his first response is "Well, it looks like one." He has to think for a moment to remember which visual clues he is responding to.

Even in the parking lot, his eye is active. He notices a byssus skipper on a milkweed flower next to his truck and excitedly points it out to us. The byssus is a true rarity, one of the specialties of Gensburg that you can't see in many other places.

Skippers are the shorebirds or fall warblers of butterflies. There are many species, and they all look alike. They are small--wingspans usually range from an inch to an inch and a half--and colored in various shades of brown and tawny orange arranged in obscure patterns. When you can make quick identifications of skippers, you have arrived as a butterfly expert.

The caterpillars of skippers feed on grasses and sedges. Some are quite catholic in their tastes, but others are tied to a particular genus or even a single species. The byssus, Panzer thinks, feeds exclusively on big bluestem grass, a dominant plant of our native prairies. Two hundred years ago, when big bluestem was one of the most common plants in Illinois, the byssus skipper was probably one of the most common butterflies. The nearly total destruction of our native grasslands has made it rare.

The heart of our morning lesson was a walk through the prairie. Panzer took the lead, and his partner Don Stillwaugh brought up the rear. Gensburg is famous for its great assortment of butterflies, and they were out in numbers for us. We counted--thanks to two pairs of expert eyes--15 species in the course of an hour, along with four interesting moths, some nice beetles, and a very rare katydid.

We saw two kinds of fritillaries, orange-and-black butterflies that are among the largest and showiest we have. Panzer told us of a girl who came along on a tour he gave of the prairie. She was wearing orange socks, and the fritillaries were all attracted to the color. She walked surrounded by butterflies.

We saw a viceroy, a species that mimics the monarch. Birds avoid eating monarchs because they taste bad. The viceroy's mimicry presumably saves it from being eaten.

One short stretch of the path was bordered by Indian hemp, a species of dogbane, that was just coming into flower. For whatever reason, this was butterfly central. The two-spotted skipper--which may soon be declared endangered in Illinois--was there, and so were the silver-spotted skipper and the Peck's skipper. A big black swallowtail, a coral hairstreak, and an American painted lady flew by.

We found two species of hummingbird moths feeding on the dogbane flowers. These moths hover in front of flowers in the manner of hummingbirds, inserting their long proboscises into flowers in search of nectar.

Panzer trotted up and down the line of dogbane, calling out the species, while the rest of us followed after, trying to remember the names and field marks of everything we saw. I felt the scales falling from my eyes. My perceptual universe was beginning to change. Creatures that had been part of the visual background noise for me were acquiring distinctive forms, moving into the foreground. When next I look at a prairie, I will see more than I saw before.

The effects of the drought were quite noticeable at Gensburg. Many of the plants were little more than half their usual size; flowers were relatively scarce, and most of the blooms were smaller than normal. Prairie plants are very long lived, and their strategy for dealing with hard times is to hold back, to cut down the demands they make on the environment, and to wait for things to improve. However, they evolved under conditions of recurrent drought, and even this year, they look quite green.

Insects cannot hunker down and wait for rain. They have to reproduce now or not at all. It seems likely that this year's drought will cut insect populations next year and perhaps for several years to come. Butterfly monitoring gets us started on the job of tracing the changes the drought is producing.

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