Butterfly Blues
Gardeners Can Help Conserve These Most Colorful of Insects.
By Rachel Foster 3/11/04

Urban and suburban gardens are woefully short on butterflies. What can we do about it? Until recently, advice on gardening for butterflies was almost exclusively devoted to a discussion of nectar plants that attract adult butterflies. Nectar is their primary food source, and most common butterflies are relatively indiscriminate about where they get it. But the adult butterfly is just one generation in the life-cycle of its species. The larval stage we call a caterpillar does most of the growing, and so it is a much more serious eater.
Caterpillars eat leaves. The idea of butterflies sipping nectar may be a lot more appealing to the gardener than caterpillars chomping foliage, but without caterpillar food there would be no more butterflies. Gardeners might wish that the larvae of the butterflies they'd love to see will be doing their feeding somewhere else. The time has come, however, for us to face the reality that "somewhere else" is increasingly difficult to find.
Our yards typically don't provide much in the way of weeds and wildflowers, and "somewhere else" (in the Willamette Valley, that means native wetlands and savannas) has largely been replaced with the monocultures of industrial agriculture that have little to offer lepidopterans or any other wildlife. Even the remnants of wild plant communities that quite recently persisted along roadsides have been mostly wiped out by misguided highway management. Some species are so particular about what their larvae eat that relatively small efforts by gardeners might make the difference between extinction and survival for local populations.
That's the opinion of Steve Northway, a past president of the Corvallis Chapter of the Native Plant Society of Oregon (NPSO), who has written: "A truly amazing illustration of the value of backyard butterfly gardening is provided by the Monarch butterfly, our only migratory butterfly species. The Western flyway's Monarch butterflies, which must pass through the Willamette Valley, are now infrequently seen here, but if the Willamette Valley's native Showy Milkweed (Asclepias speciosa) is planted ... Monarch butterflies and their big, tiger-striped caterpillars appear almost magically."
The Monarch caterpillar feeds exclusively on milkweeds. There is another important relationship between Monarchs and milkweeds: predator defense. As Northway describes it, "While the caterpillars feed on milkweed they accumulate in their bodies a bitter, highly toxic glycoside. The milkweed glycoside stored in the caterpillar's tissues persists through metamorphosis, making the butterfly as well as the caterpillar unappetizing and poisonous to predators."
Monarchs encounter many different species of milkweed in their long migration, and several species of asclepias make acceptable caterpillar food. But Asclepias speciosa, the milkweed that was once abundant in the Willamette Valley, has a high glycoside content, and naturalists suggest that Valley butterfly gardeners should favor it. (You need starts from more than one clone to produce viable seed of your own, Northway tells me.)
One of Eugene's last good stands of Asclepias speciosus, near Chad and Crescent drives off Coburg Road, was regularly visited by Monarchs until it succumbed to development. Last fall I asked Eric Wold, founder of the local chapter of the North American Butterfly Association (NABA) if Monarchs still visit the Willamette Valley. Yes, he replied, and the Eugene-Springfield area is perhaps the best place to see them. "This year I've observed them in my own small garden (near Cal Young in North Eugene) and along I-105, near the Mohawk exit in Springfield," he said. So starting a milkweed colony is a worthy idea if you can make room for this beautiful but rather aggressive plant.
A good strategy for suburbanites who would just like to see more butterflies in the garden is to observe what sort of butterflies visit the yard and nearby places, then plant their preferred larval foods. A pocket guide, compiled by Marta Makarushka and recently published by the Eugene-Springfield Chapter of NABA will make this job a whole lot easier: It will help you identify your winged visitors, and indicates what their larvae eat. It describes 78 butterflies that occur in Lane County, and the regions where they are found.
A few common butterflies are generalists when it comes to selecting a host plant to lay their eggs on. The Painted Lady prefers thistles and checkermallow, but almost anything will do where they are lacking. Some plant groups are popular with several species, so planting them is a logical place to start. Plants of the pea family (vetch, clover and lupine for example) attract, among others, Eastern Tailed Blue, Gray Hairstreak and Orange Sulphur. (Lupines appeal to some specialists, a well: Kincaide's lupine is the exclusive host plant of the imperiled Fender's Blue.)
Checkermallows (sidalcea), are favored by Common Checkered Skipper, Painted Lady and Gray Hairstreak. Willow and alder trees support many species, including Mourning Cloak and certain swallowtails. Anise Swallowtail, though, eats members of the parsley family, which includes fennel and cow parsnip. Other native plants that support several species include bunch grasses, ceonothus, cascara and bleeding heart.
Here are some tips for encouraging butterflies to use your garden: Don't use pesticides. Adopt a relaxed attitude to caterpillars when they appear on your cultivated plants. If someone is eating your parsley, plant more next time. Leave some rough, weedy areas uncut, and enrich them with popular caterpillar foods such as pearly everlasting, thistles, vetch and lupine. Plant host plants as generously as you can: Butterflies may have to detect the plants from far away. Provide water, in the form of mud or in shallow containers with sloping sides.
Including nectar plants is easy. Butterflies especially favor flat heads (yarrow, sedum, Queen Anne's lace, daisies) or long panicles and spikes of small flowers (anise hyssop and many things in your herb garden, including mint, thyme and chives.) Let prunella, clover and daisies ornament your lawn. Native plants of particular value for nectar include camas, iris, wild onion, aster, fleabane, goldenrod, lupine, vetch and yarrow. Butterfly bush (Buddleia davidii) is a nectar plant popular with many butterflies, but naturalists discourage planting it. It is invasive, and displaces native willows essential to several native butterflies.
NABA (Eugene-Springfield Chapter) has a superb website (go to www.NABA.org and click on "Local Chapters"). It has information on Butterflies of Lane County as well as lists of native host plants and local native plant retailers.
This spring, ODA will spray 183 acres of land in the Crest Drive area of Eugene with the natural insecticide, Btk, to eradicate a suspected colony of the destructive Gypsy Moth. Agencies who use Btk for this purpose make claims that imply it is specific for Gypsy Moth, but this is not true. Not only may spraying kill moth or butterfly caterpillars of any species feeding in the area, but certain caterpillars (Tiger Swallowtail for example) are far more sensitive to Btk than is Gypsy Moth.
Sunlight degrades Btk quickly, suggesting that effects should be short-lived, yet a Michigan State University study showed that droplets of spray shielded from the sun could kill caterpillars up to 30 days after spraying. Non-lethal doses also affect the fertility of resulting adults. Paul Severns, who has studied effects of Btk on butterflies after a Dexter spraying, says there is not enough research to predict non-target effects of Btk, and suggests it would be of benefit for people who butterfly-garden to keep track of what butterflies they see and how many of each they count. The data could contribute to anecdotal records of what happens in urban spray areas.