To Attract Butterflies, Don't Kill the Caterpillars

BEFORE & AFTER: A Black swallowtail in its caterpillar and butterfly stages. (Photos: Tom Oder, caterpillar and Vicki's Nature/Flickr, butterfly).

What’s the first thought that comes to mind when you see a caterpillar in your garden? Run to the tool shed, mix up an insecticide spray and kill it before it eats holes in the leaves of your shrubs or trees?

That’s the last thing you should do, says Jeffrey Glassberg. You’re not killing a caterpillar, he contends. You’re killing a butterfly.

Glassberg, president of the North American Butterfly Association (NABA) in Morristown, N.J., doesn’t think of holes in leaves as a sign of damage. He thinks of them as a sign of success. Whether by intent or chance, those holes are an indication you have at least the start of a butterfly garden.

Planting a Butterfly Garden

A butterfly garden, says Glassberg, is one with plants that support all stages of a butterfly’s life cycle. The key stages in that life cycle are the caterpillar stage and the adult nectar-feeding stage. But, to attract and keep butterflies, you can’t plant just any plant. You have to plant caterpillar plants, he emphasizes.

What Are Caterpillar Plants?

“Many caterpillars only feed on one specific plant,” Glassberg says. “Most female butterflies lay their eggs on or near that plant. If you don’t have that plant, which sometimes can be the same plant as the nectar plant but more often is a different plant, you won’t get that butterfly.”

Scientists would call the plants that caterpillars feed on “larval host plants.” Glassberg thinks that term just confuses the public, so he calls them, simply, caterpillar plants.

He says pipevine (Aristolochia tomentosa) is an example of a caterpillar plant. “If you want to attract the pipevine swallowtail (Battus philenor ) to lay its eggs in your garden, you have to plant pipevine, the host plant for the pipevine swallowtail caterpillar,” he explains. (In the photo at right, a pipevine swallowtail deposits eggs on pipevine.)

Passion flower, he says, is another example. If you want the Gulf fritillary (Agraulis vanillae) to lay eggs in your garden, you have to plant a species of passion flower such as maypop (Passiflora incarnata), yellow passionflower (P. lutea) or running pop (P. foetida). The Gulf fritillary caterpillar feeds exclusively on these plants.

“Beautiful plants like roses are like a movie set to butterflies,” Glassberg says. “Caterpillars don’t feed on them, so they don’t have any functionality for butterflies.”

Because butterflies will feed on many types of nectar plants they don’t lay eggs on, butterflies will flutter into your garden even if you don’t have that butterfly’s specific caterpillar plant. “But, if you aren’t growing caterpillar plants, you don’t have a true butterfly garden,” says Glassberg. “And that,” he contends, “takes the fun out of attracting butterflies.”

Creating Areas for Puddling and Basking

Two other elements that are often included in a butterfly garden are puddling and basking areas. A puddling area is a depression filled with water where male butterflies congregate to obtain salts and amino acids. A basking area is often a large rock where butterflies can warm their wings. (The photo at right shows Raja Brooke butterflies puddling.)

Neither is critical, says Glassberg, especially the basking area. Butterflies, he says, will find sources of water and places to bask just fine without gardeners supplying these. They’ll also overwinter in crevices in trees, rocks and even homes. However, tall, decorative butterfly houses featuring a series of narrow slits sold by garden centers, while pretty, provide no functionality in attracting or keeping butterflies, he notes.

The most important elements, he stresses, are plants that provide nectar to give adult butterflies energy and plants that provide hosts for the butterfly to lay eggs on or near and for the caterpillars to feed on. Those plants, in general, should be native to your region because the great majority of the 700-plus species of butterflies in the United States live where we see them, according to Glassberg.

Knowing Which Butterflies to Attract

The NABA has created a guide for many areas of the country that answers those questions. The region-by-region guides provide detailed lists of:

  • Each area’s top nectar flowers
  • Nectar flowers that don’t work in the region
  • The locale’s most frequently seen plants caterpillars feed on
  • Common and unusual butterflies in the area
  • General comments about butterfly gardening in the region

By gardening with the plants in the guide, Glassberg stresses, gardeners will help to increase the butterfly population. That’s important, he says, because the number of butterflies is decreasing every day.

“If a strip mall replaces a meadow, for example, the butterfly population in the meadow won’t relocate to a nearby habitat because that habitat will already be full,” Glassberg says. “That population is just gone.”

Some butterflies do migrate and can be attracted to the garden during their migrations. The monarch is a classic example and a favorite of many gardeners. It can be found in most states with the exception of the northwestern states because few milkweeds, the caterpillar host plant for monarchs, grow there.

The eastern populations of monarchs respond to the decreasing daylight length and cooler night temperatures of late summer and fall and begin flying south/southwest “toward the sun” from New England, the Great Lakes area and southern Canada, says Ina Warren, one of a dozen national conservation specialists for Monarch Watch and author of the upcoming book, “The Monarchs and Milkweeds Almanac.” These monarchs likely are headed to central Mexico to the high-elevation fir forests in the states of Michoacan and Mexico, where they will overwinter until around the first of March, she says.

East Coast

East Coast gardeners who want to provide way stations to help them fuel up on nectar during their long journey should begin looking for them on sunny days around Labor Day. Some seem to migrate on thermals down the southern Appalachians across North Georgia, Alabama and Mississippi and then hug the Gulf Coast to Texas, the best place to see them as it is the migration gateway to Mexico, says Warren.

They don’t fly at night, or in the rain. To attract them from their roosts to the garden, include fall flowering plants such as asters, goldenrods, Joe Pye weed, thistles (in photo at right) and ironweed in the landscape, Warren advises.

Gardeners in South Georgia and Florida may find them in their gardens all winter. Whether they were blown off course by fall storms is unknown, Warren says.

West Coast

The western monarchs respond in a similar way in the fall, she says. They leave British Columbia, Washington, Oregon and a few other western states when flowers begin wilting into winter dormancy and head to coastal areas in south central California, she says. They overwinter primarily in eucalyptus trees until early spring.

Monarchs tend to mate just before leaving Mexico in March. It is a time when all female monarchs, including those in California, will be desperately looking for milkweed to lay their eggs on before they die.

Almost any flower in the spring garden will provide a good nectar source for monarchs. The exceptions are plants such as hybrid roses that have had the nectaries bred out of them to extend their useful shelf life for florists, Warren says.

Warren's recommended spring nectary plant list includes almost all natives and many annuals such as zinnias (shown at right), impatiens, petunias, lantanas and Buddleja. The latter is a nectar-laden plant often sold as the “butterfly bush” that Warren calls an ideal fly-by-day fast food café for monarchs and other butterflies.

Humans' Role in Butterfly Survival

“It can't be stressed enough how important a role gardeners play in the survival of the monarchs in both the fall and spring,” she says. “By planting lots of nectar plants — whether hanging baskets, garden plants or flowering shrubs and trees and, hopefully, mostly native species — gardeners are providing the life-giving nectar that will mean the difference between life and death for migrating monarchs.”

And that’s something to think about when you see holes in the leaves of plants in the garden.