Giving butterflies a reason to stay
July 28, 2022 | View PDF
Fragile, beautiful, and fascinating, butterflies flutter their way into our gardens and seem to just as quickly wing their way out.
It isn't because they necessarily want to leave, said Heather Stoven, an entomologist with the Oregon State University Extension Service. Rather they don't find what they need to park themselves permanently.
As detailed in Extension's publication The Wildlife Garden: How to Create a Butterfly Garden, butterflies require specific room and board to have their needs met. As with all wildlife, shelter, water, and food are a given, but for butterflies, the range of repast is more limited.
When butterflies change from egg to larvae or caterpillar, they come out ravenous and with chewing mouthparts, two things that set them up to damage plants, a condition gardeners must tolerate or forgo butterflies except in the most ephemeral way.
Fortunately for the gardener – not at all fortunate for the butterfly – only a few plants qualify as nutrition for the caterpillar, sometimes just one. These host plants must be present, Stoven pointed out, or the caterpillars starve to death. (See below for some common butterflies and their preferences.)
"If you see a weird worm creeping along one of your plants, don't kill it until you have identified it," she said. "It may well be a butterfly caterpillar, maybe a rare one that you didn't expect."
To identify the caterpillar take it to your county Extension office where a master gardener will help. Or snap a good photo and submit it along with your question to the Ask an Expert feature.
In addition to adding host plants - and tolerating the caterpillars' nibbling – you'll need to plant some of the nectar plants favored by adults. Many of these – zinnias, various daisies, asters, goldenrod and milkweed – may already have a place in the garden. Since butterflies are nearsighted, Stoven said, it's best to plant one color of one species in a swath; a block of blue asters for swallowtails or a yellow moon of goldenrod for red admirals.
Fragrance plays a part, too, so don't forget the sweet smells of lavender, mint, sweet William and honeysuckle. Around the nectar and host plants, it's important to provide taller plants to act as protection from wind. During winter, shelter becomes more important for hibernating adults and caterpillars, who like to live in crevices in trees, walls, under mulch or leaf letter, even in empty sheds.
And somewhere there must be a sunny spot for the butterflies to warm their blood. They rarely take flight when temperatures are below 60 degrees, Stoven said. Water, too, is essential. Design a butterfly puddle by sinking a shallow dish right up to the lip in the ground and fill it almost to the top with wet sand, which they'll sip from.
And the usual reminder: Using chemicals in the garden is counterproductive when trying to attract wildlife.
Though the focus recently is on the monarch, Stoven noted that not much is known about the western monarch and its migration, which could be why not many are seen on the west side of the Cascades. That doesn't make planting native milkweed, monarchs' only host plant, any less important.
"I certainly doesn't hurt to plant milkweed just in case," she said. "But it makes more sense to plant it for other types of butterflies that are native to this area as well."
A partial list of butterflies seen this time of year and their hosts and nectar plants
Western tiger swallowtail
Host plants: big-leaf maple, willow, aspen, cottonwood
Nectar plants: common lilac, rhododendron, honeysuckle, milkweed, mock orange, sweet William, lavender, verbena, asters
Host plants: buckbrush, cherry, plum, hawthorn, cascara, oceanspray
Nectar plants: oceanspray, columbine, garden mint, thistle, blackberry, penstemon, sweet William, asters
Host plants: pine, Douglas-fir, true fir, hemlock, redcedar
Nectar plants: dusty miller, daisies, coreopsis, lobelia, goldenrod, strawflower
Host plant: stinging nettle
Nectar plants: daisy, aster, thistle, dandelion, goldenrod, milkweed, fireweed
Host plants: mostly thistle, sunflower, pearly everlasting, hollyhock
Nectar plants: Oregon grape, rabbitbush, zinnia, dandelion, aster, cosmos, milkweed, purple coneflower
Great spangled fritillary
Host plant: violet
Nectar plants: gloriosa daisy, thistle, verbena, milkweed
Host plant: milkweed
Nectar plants: milkweed, lantana, lilac, cosmos, goldenrod, zinnia
Host plant: grasses
Nectar plants: bluebeard, lavender, oxeye daisy, garden sage, pearly everlasting, black-eyed Susan, aster