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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

June 1996

Where painted ladies lunch and emperors dine

Plant hosts offer sustenance to Wisconsin's hungry caterpillars and can make the difference between the survival or decline of many butterfly species.

Anita Carpenter

Walk in a summer meadow ablaze with flowers and monarch butterflies will float all around you. Stroll along a sun-dappled woodland trail and mourning cloaks will flit about your face. Slosh through a wet meadow and silver-bordered fritillaries will defend their territories from your intrusion. High-step in a bog and bog coppers will scatter from your approach. Tend your garden and cabbage whites will watch you work.

Butterflies are everywhere. Some, like the monarch, are common. You'll see them flying lazily above meadows, drifting through towns, sailing over highways. Other butterflies, like the swamp metalmark, are restricted to very specific habitats. It's unlikely you would get a glimpse of one unless you made a special effort to seek out their haunts.

What determines where butterflies are likely to be found? To find the answer, look at another stage in the butterfly's life cycle. Butterflies progress through four stages: from egg, to larva or caterpillar, to pupa and finally to free-flying adult. The female adult butterfly is choosy; she only deposits her eggs on or near plants upon which the larvae will feed. These plants, called larval host plants, are specific for each butterfly species. If the plant is common, like milkweed, a host plant for the monarch, the butterfly species is likely to be common. If the host plant is uncommon, rare or restricted to a specific habitat, so is the butterfly.

Planting the host plant doesn't guarantee the butterfly will come, but without host plants, there can be no butterflies. That's why, when a butterfly is listed as a threatened or endangered species, its larval host plant is also protected.

The hosts with the most

Which host plants satisfy the needs of the 130 butterfly species regularly drifting, darting, fluttering and floating over Wisconsin each year? You might be surprised at the diversity of plant species butterflies choose to use. The menu includes deciduous and evergreen trees, shrubs, flowers and so-called "weeds."

Most Wisconsin tree species and many shrubs host butterflies. Black and pin cherry leaves are the favorite food of the larvae of the easily-recognized eastern tiger swallowtail (Papilio glaucus), a five-inch large yellow butterfly with black stripes. Its elusive two-inch green caterpillar with two orange eye spots and a yellow band feeds primarily at night, high in the tree tops, and hides during the day in rolled-up leaf shelters. Larvae of the red-spotted purple (Limenitis arthemis astyanax), a four-inch black butterfly with iridescent blue scaling on the upper hind wings and red spots on its underwings, prefers cherry, as does the coral hairstreak (Satyrium titus), a quarter-sized butterfly whose brown wings are highlighted with a row of red-orange squares. The larvae of the striped hairstreak (Satyrium liparops) dine on cherry and wild plum leaves.

The bright yellow swallowtail of northern Wisconsin is the Canadian tiger swallowtail (Papilio canadensis). Poplars and aspens lose a few of their leaves to these hungry larvae as well as to the caterpillars of the red-spotted purple and its subspecies, the white admiral (Limenitis arthemis arthemis) – the black butterfly with the broad white stripe across its wings. Larvae of the dreamy duskywing (Erynnis icelus), an easily overlooked and difficult to identify gray-brown butterfly, also eat aspen and poplar leaves.

Oak trees host munching caterpillars of two of our less conspicuous butterflies. The scrubby red oaks of central Wisconsin provide food for the larvae of Edward's (Satyrium edwardsii), and banded (Satyrium calanus) hairstreaks, two quarter-sized gray-brown butterflies. The adults fly mostly in July. Eggs are laid on oak twigs in summer and hatch the following spring. The young larvae first feed on catkins, then switch to young leaves. Edward's hairstreaks may also feed on black oak, while banded hairstreaks choose white oak.

Several butterfly species prefer willows. The shrubby willows of wet meadows are chosen by Acadian hairstreaks (Satyrium acadica). The mourning cloak (Nymphalis antiopa), a common four-inch beauty with chocolate brown wings edged with a creamy band, is not as fussy. It prefers willow, but the larvae will feed on American elm, paper birch, aspen and hackberry. Mourning cloak larvae are one of the few species to feed communally. Females lay yellow eggs in a cluster around a small branch. The spiny black caterpillars with the red prolegs are easily identified, and ravenous – they may defoliate a good portion of the willow. Do not be alarmed, and do not kill the larvae. Soon they'll crawl off the plant to pupate. The tree quickly responds by putting forth new growth.

The viceroy (Limenitis archippus), the orange mimic of the monarch, lays her eggs on the leaf tips of willows. The brown larvae with a white saddle and two short bristly horns are identical to red-spotted purple and white admiral larvae. There is some overlap in host plant preference, so the larvae can be reliably identified only after they've transformed into butterflies.

Hackberry is a southern tree whose range extends north into southern Wisconsin and along the Mississippi River valley. Hackberry emperors (Asterocampa celtis) dine on – you guessed it – hackberry leaves. Eggs are laid on the underside of leaves. Half-grown larvae overwinter attached to the leaves, which naturally fall to earth. In spring the young caterpillars must climb the tree before munching on the new year's leaf growth. If you'd like to help the hackberry emperors that visit your yard, do them (and yourself) a favor by not raking up fallen leaves in autumn. The tawny emperor (Asterocampa clyton), and the American snout (Libytheana bachmanni), a stray visitor to Wisconsin, also use hackberry as a host plant.

Black locust is the sole host plant for Wisconsin's largest skipper, the silver-spotted skipper (Epargyreus clarus). After the female locates a suitable black locust, she lays each of her eggs on a nearby plant. After hatching, the young, hungry yellow-green slug-like larva with the large black head must search for the proper host. If it is successful, the larva feeds on black locust leaves at night and hides in a leaf shelter during the day.

A stand of prickly ash can be a nightmare to walk through but as you struggle, remember that this plant hosts Wisconsin's largest butterfly, the giant swallowtail (Papilio cresphontes). This impressive six-inch butterfly has black wings with a broad horizontal yellow stripe and a row of yellow spots along the trailing edges. The mature two-and-a half-inch brown-and-white larvae resemble bird droppings, to deceive and discourage hungry predators. As with most caterpillars, swallowtail larvae feed at night and are not easily found.

Evergreens also host butterfly larvae. The eastern pine elfin (Callophrys niphon), one of Wisconsin's smallest butterflies, lays her eggs on developing needle clusters of jack, red and white pines. The larvae feed on young needles. Little is known about the life history of bog elfins (Callophrys lanoraieensis), a tiny inhabitant of black spruce-tamarack-sphagnum bogs of northern Wisconsin, except that black spruce is its host plant. The olive hairstreak (Callophrys gryneus gryneus), Wisconsin's only iridescent green butterfly, feeds exclusively on red cedar or juniper. Although red cedar is common, the little butterfly is not.

Finding favor with flowers

Many butterflies select flowers for host plants. There's a cozy relationship between milkweed and monarch butterflies (Danaus plexippus). The female lays her eggs singly on tender leaves, sometimes on the upper surface but most often on the underside. The eggs hatch in four days and the yellow-, white- and black-striped caterpillars satisfy a voracious appetite by chomping on leaves.

A large green caterpillar with black stripes and yellow spots frequently appears in gardens on dill, parsley and carrot. Have you ever wondered what this caterpillar becomes? Your yard has been blessed with a visit by a wandering black swallowtail (Papilio polyxenes), a four-inch black beauty with a yellow band along its wings. Make room for a few extra plants and let the caterpillar feed and live. In the wild, black swallowtails feed on wild carrot, wild parsnip and golden alexander.

Another garden visitor is the cabbage white (Pieris rapae), an exotic or nonnative species. The slender green caterpillars with the lateral yellow stripe bedevil gardeners by munching on cabbage and broccoli.

Two native white butterflies found in sandy habitats, the Olympia marble (Euchloe olympia), and mustard white (Pieris napi), nectar on the tiny, four-petaled white blossoms of rock cress, a diminutive six-inch plant, also a member of the Cruciferae. Later the butterflies lay their yellow eggs singly on rock cress leaves, which the larvae consume.

The silvery blue butterfly (Glaucopsyche lygdamus) lays its eggs singly in the developing blossoms of wild pea. After the eggs hatch, the one-half inch, slug-shaped larvae feed on the lavender flowers. Often the larvae are tended by ants that drink the sugary dew the larvae secrete. In return, the ants probably provide some protection for the caterpillars from hungry predators and parasitic wasps.

Wild lupine, with its beautiful spikes of blue flowers, hosts the federally endangered Karner blue butterfly (Lycaeides melissa samuelis). Females lay eggs on lupine leaves and blossoms, which become food for the slug-shaped larvae. Two rarer butterflies, the Persius duskywing (Erynnis persius), and frosted elfin (Callophrys irus), also depend solely on lupine.

Violets are hosts for many orange-colored fritillaries. Silver-bordered fritillaries (Bolaria selene) feed on violets in slightly drier meadows. The very common great-spangled fritillary (Speyeria cybele) chomps on violets found in open moist areas, but this butterfly is a wanderer – it may be found in habitats not often populated with violets. The rare Wisconsin-endangered regal fritillary (Speyeria idalia), a prairie butterfly, prefers bird's-foot violet. Characteristically, fritillaries lay their eggs singly on plants near a violet. The young larvae must find their way to the correct plant. Some fritillary larvae begin feeding after they hatch in summer while others do not. All overwinter as immature larvae and resume feeding the following spring when tender violet leaves are available. The bog fritillary (Bolaria eunomia) of northern Wisconsin departs from the usual violet fare and feeds on willow.

Other flowers that are used as host plants include sunflowers and asters by Gorgone checkerspots, (Chlosyne gorgone); turtlehead by Baltimore checkerspots (Euphydryas phaeton); bearberry by Hoary elfins (Callophrys polios); asters by pearl crescents (Phyciodes tharos); wild indigo by wind indigo duskywings (Erynnis baptisiae); leatherleaf and Labrador tea by brown elfins (Callophrys augustinus); blueberry by Henry's elfins (Callophrys henrici); everlasting and pussy toes by American ladies (Vanessa virginiensis); and native cranberries by bog coppers (Lycaena epixanthe). The northern blue (Lycaeides idas), a Wisconsin endangered species, feeds on dwarf bilberry, a member of the blueberry family and a Wisconsin threatened species.

Don't pull that thistle!

Some of our most common and widespread butterflies use plants we consider to be weeds. Have you removed stinging nettles from your yard? The eastern comma (Polygonia comma) and question mark (Polygonia interrogationis), two orange and dark brown anglewing butterflies, choose nettles. The larvae of the Milbert's tortoiseshell (Nymphalis milberti), a two-inch brown butterfly with a bright orange and yellow band, feed communally on nettles. The unmistakable red admiral (Vanessa atalanta), a two-inch brown butterfly with an orange-red band across its wings, feeds on nettles. All these butterflies are wanderers and may find your nettle patch and reproduce. Their colorful wings brighten any yard.

Thistles are another plant we can't seem to appreciate. Thistles are wonderful, not only as rich nectar sources for butterflies but as host plants. Thistles of all kinds are devoured by larvae of painted ladies (Vanessa cardui), whereas the swamp metalmark (Calephelis mutica), a state threatened species, is a thistle connoisseur, feeding only on swamp thistle (Cirsium muticum), itself a state threatened species.

Other unassuming plants butterflies use include sheep sorrel by American coppers (Lycaena phlaeas), curly dock by bronze coppers (Lycaena hyllus), and plantain by common buckeyes (Junonia coenia). Grasses are the preferred food of common wood-nymphs (Cercyonis pegala), little wood-satyrs (Megisto cymela), and skippers. Sedges are chosen by eyed browns (Satyrodes eurydice) and other skippers.

Protect plants, save butterflies

Butterflies do little damage to host plants. Most species lay single eggs on the chosen host. When the hungry caterpillar finishes eating and wanders off to pupate, the plant recovers.

Some common butterflies are generalists, like the mourning cloak. They are able to feed on different host plants, selecting the plants available at the time. Butterfly species that can use a variety of host plants have larger populations and better chances for survival. Butterflies dependent on a single host plant face the greatest challenge for survival. Once the host plant is gone, the butterfly is lost.

Some butterflies are wanderers and may find new areas to colonize. Others, such as the swamp metalmark, are fairly sedentary, not straying far from their place of "hatch." If their habitat is altered or destroyed and the host plant is lost, there is little, if any, chance for survival.

Everyone makes choices on land and habitat use that affect the lives of butterflies. We mow roadsides when monarch caterpillars are feeding on milkweed. We remove nettles and thistles. We spray our yards for insect control. We drain and fill wetlands.

Butterflies would benefit from a little help from us. Besides planting the colorful flowers that provide nectar for adult butterflies, consider planting caterpillar hosts, too. Be willing to tolerate a few holes in violet leaves and the disappearance of willow leaves. Save yourself the effort of mowing those expansive country yards – let most of the native vegetation remain. If you find a black swallowtail caterpillar in your garden, look upon it as an opportunity to study the remarkable transformation from caterpillar to butterfly. Share the thrill with children.

Butterflies are Wisconsin's flying jewels. To enjoy their colorful wings in the future, we must look beyond their beauty and recognize that they cannot survive without a variety of plants and habitats.

A home for butterflies

Birds and bats have had them for years. Now butterflies can get in on the back yard real estate boom when you mount a butterfly house in your yard, field or garden.

The carpentry skills necessary to build a butterfly house are no more complex than those needed to construct your average bird bungalow. The narrow wooden box, about two feet in length but only three-and-a-half inches wide, has a pitched roof and several long, narrow slits cut into the front panel. A two-foot copper pipe is driven 10 inches into the ground, and the butterfly box is set on the pipe, raising the bottom of the box about eight inches above ground.

Place your butterfly house near nectar sources and larval host plants. Insert a few long twigs for roosts, and wait for the colorful tenants to arrive. It's likely you'll have a houseful in no time – butterfly habitat is decreasing and butterflies will be looking for shelter.

If your handyguy/gal skills end with the ability to open a pickle jar, the Beaver Dam Senior Citizen Center sells all-cedar butterfly houses for $12.40 inside Wisconsin (price includes shipping, handling and state sales tax), $14.00 outside Wisconsin. Write Dan Kopff, Beaver Dam Senior Citizen Center, 114 E. Third Street, Beaver Dam, WI 53916. Or call (414) 887-4639.

A garden that's all aflutter

Butterfly enthusiasts who want to see a lot in a little time should plan a summer stop at the Mosquito Hill Nature Center in New London, Wis. (northwest of Appleton). Naturalists there built a 30-by-30 foot screened-in garden to house butterflies and their host plants. The Butterfly House is open to the public on Wednesdays, Saturdays and Sundays, 11 a.m. to 3 p.m. from July 6 through Labor Day, Sept. 2. Group tours can be arranged in advance on Thursdays and Fridays. Signs along the paths clearly mark larval host plants and a guide can help you identify the 50 or so butterfly species flitting about. The center is located at N3800 Rogers Road, New London, WI 54961. Call (414) 779-6433 to find out about summer tours and events.

Anita Carpenter takes wing with Wisconsin's flying jewels in the fields, forests and gardens near her Oshkosh home.

Milk-fed monarchs

by Greg Vande Leest

While the monarch butterfly is best known for its spectacular migration to wintering grounds along the Gulf Coast and Northern Mexico, the summer show in Wisconsin is more intimate. Poke around a common milkweed and you'll likely find a voracious caterpillar munching away on the thick leaves. This food source will actually improve the monarch's chances of survival long after the caterpillar finishes feeding. Milkweed contains toxic substances that are incorporated into the monarch's body over time, making it distasteful to predators.

The caterpillar itself is a virtual eating machine, shedding its skin up to six times as it grows. After several weeks of almost continual feeding, it attaches itself to a plant stem or leaf in the characteristic "J" shape and begins to pupate, creating the familiar light-green, gold-spotted chrysalis.

Inside the chrysalis, the caterpillar continues its journey to adulthood. Since it hatched, the caterpillar has contained growth centers called "imaginal buds." Hormones secreted by glands close to the caterpillar's head inhibit the buds' growth. The shutting off of this hormone causes the caterpillar to enter the pupal phase. Now, the imaginal buds start to grow and develop into adult organs and structures. At the same time, the organs of the caterpillar gradually dissolve into a liquid substance that feeds the developing adult. All of this takes about two weeks, depending on how warm the weather is.

It's easy to tell when the adult monarch is getting ready to emerge from the chrysalis: the case becomes transparent and the butterfly can be seen inside. A short time later, the pupal skin suddenly splits open near the head and the adult butterfly emerges. Its wings are in no way ready for flight, as they are still crumpled and moist from being wrapped inside the chrysalis. The monarch moves to a sheltered spot where it can hang upside down, to dry its wings and swallow air. This pumps fluid into the veins of the wings and causes them to expand fully.

After several hours the wings will have hardened, and the monarch can then fly away. Depending on the time of year, the adult will either feed on nectar for a short time and then lay eggs (if female), or it will begin the arduous journey to the wintering grounds hundreds of miles away.