© Janet Davis

It's always an auspicious occasion, that warm afternoon in early summer when the season's first swallowtail butterfly sails lazily over my back fence looking for lunch. With black, tiger-like stripes on his yellow fore wings (many females have a black wing phase) and jewelled spangles of blue, black and orange on his hind wings, the Eastern tiger swallowtail, Papilio glaucus, is nothing short of majestic as he lights gracefully on the bristly, orange center of a big purple coneflower.

Butterfly watching is one of the great joys of tending a garden, but not all gardeners understand that these lovely guests are discriminating visitors; "just any old blossom" won't do. A butterfly restaurant needs to feature a diverse menu of flower colors with blue, purple, violet, pink, yellow and orange special favorites. Like bees (and unlike humans), butterflies are able to see into the ultra-violet end of the spectrum. Flowers in clusters and daisy-like flowers from the family Asteraceae are most rewarding, each bloom offering dozens of tiny, nectar-rich disk florets and an accessible, flat surface that makes for an easy landing pad and a long, comfy meal.

Members of the family Lepidoptera, butterflies rank well behind pollen-eating bees (Hymenoptera), flies (Diptera) and beetles (Coleoptera) as effective pollinators. If pollen dusts off onto their scaled wings or knobbed antennae as they move from flower to flower, it's strictly by accident. What they're really looking for is sweet stuff -- flower nectar for most species, but tree sap or overripe fruit for others. Poppies and anemones secrete no nectar, only pollen, so butterflies do not visit these plants at all.

A butterfly's proboscis -- the long, flexible, sucking tube attached to the mouth -- is an ingenious bit of natural engineering. Entomologists studying butterflies in the 1960's and 70's discovered that the proboscis is composed of two connected canals (galae) containing blood, nerves and muscles. Where the inner surfaces of the long galae join, there's a convex hollow, forming a straw-like tube running the length of the proboscis. It's through this tube that nectar passes into the butterfly's mouth.

When a butterfly flies, its proboscis stays neatly rolled up under its head; when it lands to sip nectar, it uncoils the proboscis to begin the sucking action, a knee-bend allowing it to angle into the flower. But no energy is needed to roll the proboscis up again; it's a passive action made possible by resilin, the remarkable, rubber-like protein from which it is made.

If you really want your garden to attract butterflies, you need to avoid pesticides, grow lots of nectar plants and encourage your neighbours to do likewise. Butterflies are efficient foragers, usually visiting one flower species at a time, so it stands to reason that a street filled with gardens containing nectar favorites -- asters and goldenrod in late summer, for example -- will be a popular destination. Grow uncomplicated, single blossoms since double flowers make nectar-gathering difficult, if not impossible. Native plants, particularly composite daisies and thistles, are highly effective at luring the native butterflies that have evolved with them.

Fragrant flowers attract butterflies, sweet violets and the balsam-scented panicles of butterfly bush (Buddleia davidii) being two examples. But the scent may not always be one humans enjoy (animal dung is favored by one species) or even detect. Floral perfume is used by nocturnal moths to guide them through the darkness toward night-blooming flowers, usually white in color to ensure the moths see them. For example, the white, trumpet-shaped blossoms of flowering tobacco (Nicotiana alata), native to Brazil and Argentina, open and exude their scent in evening to attract moths with the necessary long proboscises to pollinate them.

Other good nectar plants include species from the genera rudbeckia, gaillardia, liatris, verbena, cosmos, veronicastrum, silphium, solidago, ratibida, heliotropium, eupatirum, lantana, tagetes, tithonia, aster, vernonia, scabiosa, Echinacea, sedum, helianthus, cirsium, monarda and zinnia.

Butterflies are most active on windless days in late morning and afternoon, after early dew has evaporated, humidity has lessened and the sun has warmed flower nectar, making it sweeter and thicker. Nectar is a high-energy food whose sugar content, a combination of sucrose, fructose and glucose, generally averages 40%, but can reach 75% in plants like marjoram (Origanum vulgare).

As they forage, butterflies also look for water to drink, so it's recommended that shallow pans of water or a permanently muddy spot be provided near the nectar plants. They like to rest on a warm stone or board between nectar flights so find room for a few of those nearby too. Although butterfly houses have become popular items in recent years, there's little evidence that butterflies are actually in the market for houses.

Larval Plants:

Growing nectar plants is only half the equation in butterfly gardening. Butterflies undergo complete four-stage metamorphosis (egg, larval caterpillar, pupa or chrysalis, adult), producing two or more generations in a season. As the adult female prepares to lay her eggs, she looks for a suitable food plant to nourish the larval caterpillar. This search for a host plant is no random quest; native butterflies and their larval food have evolved together and failure to locate the appropriate plant means the butterfly must travel elsewhere to find it.

Monarch butterflies, for instance, lay their eggs on milkweed plants of the genus (Asclepias). For urban gardeners, ubiquitous common milkweed (A. syriacus) is not a good choice since it is very invasive and its ornamental value is short-lived; more desirable species include moisture-loving swamp milkweed (A. incarnata) and orange-flowered butterfly milkweed (A. tuberosum), which favors sandy soil.

So tied is the survival of monarchs to milkweed that Canadian and U.S. scientists recently raised an alarm about the link between genetically altered food plants and the beautiful black-and-orange butterfly. In parts of the American midwest where tap-rooted milkweed has long been a thorn in the farmer's side, corn and soybean crops grown from seed genetically altered to be resistant to the herbicide Round-up are thriving at the expense of the monarch caterpillar's host plant, which is killed by the herbicide. Since half the monarchs that migrate each winter to Mexico originate in this agricultural belt, the scientists' fears seem well-founded.

Other larval plants include composites like pearly everlasting for the American painted lady; umbellifers such as dill and parsley for the black and anise swallowtails; birch, wild cherry, poplar and aspen for the Eastern tiger swallowtail; willows, elms and poplars for the mourning cloak thistle, burdock and sunflower for the painted lady; and nettles, elms and hops for the question mark.

For gardeners, the challenge is to replicate the fast-disappearing natural habitat of monarchs and all butterflies in our own backyards. To nurture them, so they can nurture us.

Adapted from an article that appeared originally in President’s Choice magazine.

Read about three excellent plants for butterfly gardening.

Read two stories about butterfly houses: Montreal Botanical Garden’s Butterfly House and Niagara Parks’ Butterfly Conservatory.

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