Winter is a good time for me to start studying butterflies. In summer I get distracted and confused when the objects of my study flutter on before I am ready to identify them. If that little creature dancing on the breeze in June could wait just one more week, I would be ready to declare definitively whether it is Horace’s dusky wing or Juvenal’s dusky wing, whether it is a comma or a question mark, whether it is an Edwards’s hairstreak or a banded hairstreak. But it is gone before I can figure out what distinguishing characteristics I should be looking for.
Long ago when I first began to study birds I pasted pictures and descriptions of wood warblers on index cards and taped them to the walls of my living room along about Thanksgiving. By mid-April I was ready. When the budding trees began to fill with migrants I could recall their names as if we had grown up together.
This winter’s project is to develop that level of facility with lepidopterans. What I have now is book knowledge and the ability to identify the most common and distinctive species in the field. What I want is to be able to call the names of all the local species after only a glance. It is a project that requires book study now and lots of time in the field come spring.
Butterflies are currently rather fashionable. The Field Museum had a living display of various species last summer, and when the new Nature Museum of the Chicago Academy of Sciences opens, a living display of Illinois butterflies will be one of the permanent exhibits. Butterflies are the least yucky of insects. A friend of mine describes them as honorary birds. Show people a dung beetle industriously building a ball of fresh horse manure to feed its offspring and most will react with disgust. But a picture of tiger swallowtails eagerly drinking from a pool of warm dog urine will elicit oohs and aahs. The Greeks identified butterflies with the soul–perhaps because the metamorphosis from egg to caterpillar to chrysalis to adult suggested the soul remaining immortal through many changes of form.
Butterflies are also a relatively easy entree into the incredibly complex world of insects. North America has about 30,000 species of beetles, and it is a virtual certainty that there are species unknown to science living within the city limits of Chicago. These numbers can be intimidating to the would-be student of coleopterans. Butterflies are a much more manageable subject. Around 700 species live in North America–very close to the number of bird species–and only about 100 are found in the Chicago area. Most of these are quite habitat specific, and their seasonal distribution is a further help in identification. Butterflies don’t live very long. Juvenal’s dusky wing is a spring butterfly that you are not likely to see after June. Species that can be seen in flight from April to October are probably producing more than one brood per year. Some species, like the pipe vine swallowtail, have two broods, with a gap between them when no adults are around. Other species have as many as three broods.
Butterflies divide the essential tasks of life among their life stages. Basically, caterpillars eat and adults have sex. A caterpillar is an eating machine with tiny eyes, huge mandibles–they move from side to side, not up and down like the jaws of vertebrates–and a large gut. They have taste and smell receptors scattered all over their bodies and spinnerets and silk glands for creating nests. Many species use their silk to curl leaves into a tube, which they use as a nest.
Adults have huge eyes–useful for flying animals–and a long tubular proboscis through which they suck nectar (or dog urine). Females have chemical receptors on their front legs that they use to detect suitable host plants for their eggs.
If you want to know butterflies it helps to know plants. Only one North American butterfly is carnivorous. The caterpillars of Feniseca tarquinius, the harvester butterfly, eat aphids. However, the favored aphids show strong plant preferences, so even someone hunting for harvester larvae would need to know one plant from another.
The plant-eating caterpillars show varying degrees of fussiness. Most can live only on the plants of a particular family. Some–like the Karner blue, a federally endangered species that lives in a few sites in northwest Indiana–can eat only one species. Some, like the painted lady, can eat practically anything. Plants don’t like being eaten. They fight back by producing poisonous chemicals, so the caterpillar needs to develop defenses against the chemicals in order to survive. However, butterflies plainly evolved with flowering plants, and very few species eat ferns or conifers.
If you want to see a particular bird you need to learn what sort of habitat it favors, but the habitat can be described solely in structural terms. A grove of well-spaced large trees is a good place to look for Baltimore orioles, and it doesn’t matter much whether the trees are oaks, maples, basswoods, or elms. But if you want to find Edwards’s hairstreak butterfly, the trees have to be oaks, because that is what the caterpillar eats. The adults will be there because the males need to find females and the females need to find suitable sites to lay their eggs. For fritillaries, you need violets; for monarchs, milkweeds; for silvery blues, legumes; for Delaware skippers, big bluestem and switchgrass.
Butterflies seem much more attached to their environment than birds. According to research done by Ron Panzer of Northeastern Illinois University, about a third of our local butterfly species are so firmly attached to their environment that they cannot live outside the scattered remnants of the native landscape that have survived in the metropolis. So the Baltimore checkerspot, gaudily patterned in black, white, and orange, lives only in undisturbed wetlands. Its favored host plant, a wildflower called turtlehead, renders the insect poisonous to birds. It has no fear of predators, but an invasion of purple loosestrife or cottonwood trees can wipe it out.
Many butterflies have intriguing relationships to other animals. The Edwards’s hairstreak, a tiny insect with warm brown wings spotted along the edge of the hind wing with orange and blue, starts its life as a caterpillar eating the opening buds of oaks. But when the caterpillar reaches the later stages of its larval life, it begins spending the night eating oak leaves and the day at the foot of the tree in a chimney of leaf litter built by ants. The ants feed on honeydew, a sweet substance secreted by the caterpillar, and in return protect the larva from predators.
You can find stories like this throughout the literature on butterflies. If you consult references, you will also find all sorts of gaps in our knowledge of even quite common and widespread insects. Basic life-history information is missing. Does this animal hibernate as an egg, larva, pupa, or adult? In many cases we don’t know. It would be good to have more people out there looking.
There was a time when nearly all butterfly study was done on dead insects. You captured the hapless creature in your net, stuck it in a bottle with some potassium cyanide, and once it was dead, impaled it on a pin and stuck it in a glass-topped box.
Some collecting is still necessary, but there is much more emphasis now on observing live animals. This means that the observer has to be able to make a reliable identification without the help of potassium cyanide. Bird-watching went through a similar transition in the early years of the 20th century. Contemporary birders have compiled an enormous body of lore on field identification, discovering clues that no one knew of in 1920. Butterfly identification is in the early stages of this process, though quite a bit is already known. Of course, the Chicago area is leading the way.
About 15 years ago Panzer developed a simple protocol for monitoring butterfly populations. With training, interested amateurs were able to do this work reliably. Volunteers were enlisted, and because of them we now have data–some of it going back 15 years–from many sites in the region. For the past several years the Butterfly Network has been overseen by Douglas Taron, the man in charge of creating the butterfly exhibit at the new Nature Museum. The network is a prime example of what has become a Chicago specialty. It combines the enthusiasm–and willingness to work for nothing–of volunteers with the expertise of trained scientists. It provides the scientists with data they could not otherwise have and gives the volunteers the chance to participate directly in a worldwide effort to understand and protect nature.
I am hoping to be ready to take part in the Butterfly Network next summer. I look forward to the opportunity to explore areas I have only dipped into in the past. I also like the hours. After years of dragging myself off to the woods in the predawn darkness to survey nesting birds, it will be a treat to start keeping butterfly hours. These humane insects don’t start moving around until the sun has warmed things up. Bird surveys usually start about 5 AM. Butterfly surveys can start at 11.