Shelter Island Greener Gardens: Raising Butterflies

Last week, while having lunch outdoors, I spotted a spring azure, a small butterfly with lovely violet wings. Its welcome appearance marks the start of a long season of butterflies (and moths) that visit and reproduce in my yard.

Raising butterflies is easy if you meet their basic needs — nectar and host plants. In order to encourage imperiled monarchs, I’ve planted butterfly weed (Asclepias tuberosa) because milkweed species are their only larval host.

The monarch has evolved so its larvae can consume the toxic milkweed leaves without harm. This toxicity stays with the adults who advertise their bad taste to birds with their distinctive orange and black colors. In my garden, butterfly weed has self-seeded so much that for several weeks in late June into July, areas are ablaze with its orange flowers. If all goes well, the large, handsomely striped caterpillars survive to metamorphose into adults.

Goldenrods (Solidago species) are another multi-purpose perennial that should be a staple of every garden. According to entomologist and author Douglas W. Tallamy’s terrific book, “Nature’s Best Hope,” goldenrod “leaves support 110 species of caterpillars” in his southeast Pennsylvania region.

As an extra benefit, “its flowers provide pollen and nectar to 35 bee species, 15 of which use only goldenrod pollen.” (Myth buster alert: as an insect-pollinated plant, goldenrod does not cause hay fever.) Native asters are another essential host and nectar perennial.

The spring azure thrives in my garden because I grow several viburnum species. I planted spice bush (Lindera benzoin) because it’s a host for the charismatic spice bush swallowtail. Field pussytoes (Antennaria neglecta), a diminutive ground cover that endures my dry soil, is host to the American lady butterfly.

The shadbush (Amelanchier species), sweetfern (Comptonia peregrina), and summersweet (Clethra alnifolia) that border the path to our house host a number of butterflies and moths. The slightly chewed leaves on shrubs and trees are a sign that my little ecosystem is working.

Our abundant oak, hickory, and black cherry trees also play an important role as hosts. Oaks in particular host hundreds of caterpillar species. The non-native Buddleia is a good nectar source but it’s a larval host to only one butterfly species. (It’s also becoming invasive in some states.) Likewise, a perennial lantana in my garden is a butterfly and hummingbird magnet but not a larval host. 

Caterpillars are also a crucial component of the food chain, especially for birds and their young. One study estimated that chickadee parents collect up to 600 caterpillars per day to feed their chicks. If you want birds, embrace caterpillars. You might also discover they’re often beautiful and wondrously strange. 

Aside from host plants and nectar, caterpillars have other easily attained requirements: avoid using pesticides, leave some leaf piles in unused places for overwintering pupae, and replace lawn under trees and create leafy areas or shade gardens so caterpillars have a safe, mower-free place to construct their chrysalises or hibernate. 

Dan Gilrein, Cornell’s Suffolk County Extension Entomologist, recently suggested landscape designers create “caterpillar gardens” for clients interested in enhancing butterfly populations (https://www.e-gro.org/pdf/2023-12-27.pdf). We can do the same.

Butterflies delight us. We should return the favor by supporting them throughout their life cycle.