A recent study of declining butterfly populations published in the journal Science made headlines across the country when it came out in March. The New York Times even launched an interactive tool so readers could see how butterflies had been impacted in their specific area. In the abstract of their findings the scientists concluded that “the prevalence of declines throughout all regions in the United States highlights an urgent need to protect butterflies from further losses.” So, what’s a gardener to do?

Plant caterpillar food, says Mary Anne Borge, the editor of Butterfly Gardener, a publication put out by the North American Butterfly Association for its members. When gardeners think about supporting butterflies, “we always think about providing nectar for butterflies for the adult butterflies,” says Borge. “And we think of other critters that might munch on the leaves of plants as pests. But butterflies are not butterflies through their whole lifecycle. They are caterpillars first. So if you really want to help butterflies, you really need to provide not just nectar for the adults, but you also have to provide food for the caterpillars.”

And it turns out, caterpillars are also very particular about what they can eat.

Butterflies strategically lay their eggs on particular plants, so that when their caterpillars hatch they will find themselves on a plant they can digest. The best known example of this host plant and caterpillar relationship is the milkweed-monarch connection (in part because monarchs are so distinctive and they can eat only from the milkweed group), but there are many such relationships. Some caterpillars, like monarchs, can eat only one plant, while others can happily feast on a dozen, but caterpillars can rarely eat ornamentals imported from abroad.

What you plant to feed your regional caterpillars will, therefore, depend on where you live. The National Wildlife Federation has a plant finder tool where you can plug in your zip code and search for butterflies and get a list of their host plants you might use in your garden. But Borge also suggests gardeners keep an eye out for butterflies slightly outside of their region, too. “I found it very interesting to actually look at the regional data from that report in Science. There are some interesting trends that they hint at in the writeup for the study: Butterflies that historically have had a pretty decent population in the southern United States who are now increasing their numbers in the north,” says Borge. “The only thing that enables that is having the caterpillar food plants that they need.”  

When selecting plants for caterpillars, Borge warns to be careful with cultivars. “If you change the leaf color, that means that you’re actually changing the chemical composition of those leaves, which may make them not digestible for the caterpillars.” She cites the example of a cultivar of ninebark called ‘Diablo’ that changes the leaf color from green to more of a reddish shade. “It’s highly unlikely then that those leaves will still be compatible with the digestive system of the spring Azure butterflies that use it as a host plant.”

If you want to support butterflies and caterpillars, you have another reason to tackle invasives in your yard. Borge says that in some instances a foreign plant can fool a butterfly into thinking it is its native host plant. For example, the West Virginia white butterfly specializes on native mustards, like cut-leaf toothwort, and the adult butterfly females can be fooled into laying their eggs on the notoriously invasive garlic mustard (Alliaria petiolata). “But when the caterpillars hatch, they can’t adjust or thrive on that food,” says Borge.

Here are a few butterflies and their host plants that Borge, who is based in New Jersey, encourages gardeners to consider:

Sleepy Orange & Wild Senna

An example of a butterfly-plant pairing that was at one time slightly out of range for Borge. As recently as 20 years ago, sleepy orange were thought not to be able to survive the winters further north than North Carolina. Because wild senna was present at Bowman Hill Wildflower Preserve, where she volunteers, they began spotting sleepy orange. Now sleepy orange is commonly seen in New Jersey and Pennsylvania during the mid-summer butterfly counts sponsored by NABA.

Spiecebush Swallowtail & Common Spicebush

The striking black spicebush swallowtail depends on, you guessed it: spicebush (Lindera benzoin), which is a native understory shrub. Butterflies are often named for their host plants. Borge has spicebush plants in her own shade garden. 

Black Swallowtails & Umbellifers

The black swallowtail specializes in the Apiaceae family of aromatic flowering plants, but it’s not picky about whether those plants are native or not. It can eat golden Alexander, a native member of the umbellifer family, but they’ll also feed on cilantro, parsley, dill, fennel, Queen Ann’s lace, and other imported plants. “That’s more unusual that a butterfly caterpillar would eat plants that are not native; typically they need to be native,” notes Borge.

Eastern Tiger Swallowtail & Wild Cherry

“Eastern tiger swallowtail uses several different trees as a caterpillar food, one of which is the ash tree, which you probably know have been dying because of the emerald ash borer,” explains Borge. Luckily, the eastern tiger swallowtail is not as picky as some butterflies. It can also use tuliptrees and wild cherry trees (Prunus serotina) as its host plant. “They have beautiful flowers typically in May,” Borge notes.

Pipevine Swallowtail & Pipevine

Another butterfly named for its host plant is the pipevine swallowtail, which is named after its Dutchman pipe (or pipevine), a native vine. Borge notes you have to plant a good amount of a host plant, so that there is enough that the butterflies can find it. “It’s a beautiful butterfly: It’s dark and has gorgeous blue on the lower parts of its wings.”

Emperor Butterfly & Hackberry

Borge notes that the native hackberry tree (Celtis occidentalis) hosts two large butterflies, the hackberry emperor and the tawny emperor, but it’s also a powerhouse host to more than 40 other species of butterflies and moths.

Zebra Swallowtail & Pawpaw

The black and white striped zebra swallowtail’s only host plant is the Pawpaw tree, the northernmost member of the custard apple family, Annonaceae, which is also beloved by human foragers like our own Marie Viljoen.

See also:

• Monarch Butterflies Are Nearing Extinction: 5 Ways to Help
• Gardening 101: Milkweed
• Here’s How You Can Help Save Nature With Your Yard