The eastern tiger swallowtail (Papilio glaucus) is quite common in our region. It’s no less beautiful for its abundance. These beauties can be seen in virtually any meadow, stream bed, or other open area from Spring through early Fall. They are one of the more photogenic butterflies because of their size, coloration, and relatively relaxed movement. Along with the cabbage white, they are some of the most frequent visitors to my butterfly garden.
I recall referring to them decades ago as “yellow swallowtails” as distinguished from “black swallowtails.” I’m not sure if this was a regional colloquialism or my own failing; either way it’s confusing. The eastern tiger swallowtail has both a yellow and a black morph, and several local species of swallowtail are predominantly black. Black swallowtail is actually the common name of one of them. In parts of the Mid-Atlantic, it overlaps with the similar Appalachian tiger swallowtail (Papilio appalachiensis) and the giant swallowtail (Papilio cresphontes). The latter is fairly easy to identify by multiple characteristics, including its giantry. The former is a bit tricky and requires close observation of the trailing edge of the ventral forewing. The row of yellow dots found on the eastern is more of a continuous bar on the Appalachian.
Host plants include a variety of trees and bushes: tulip poplar, common lilac, black cherry, and species of ash and willow, for example. Many of these are common in the mid-Atlantic both as naturally occurring plants and as native ornamentals.
The adults will feed on just about any plant for nectar. I frequently find them on my butterfly bushes (my one non-native concession inside the butterfly garden) and they seem to love buttonbush (Cephalanthus occidentalis) as well. I’ve also seen them feeding from coneflowers, bee balm, thistles, Queen Anne’s Lace, and more. They seem willing to give a chance to any flower large enough to support them while they feed.
Planting a butterfly garden was one of my first landscaping priorities after moving into my home in 2014. On one level, this was motivated by the idea that butterflies are pretty, and it would therefore be cool to see a lot of them often. This is true, and a perfectly fine motivation, but “butterfly garden” is a bit of a misnomer, at least in terms of the endgame. Butterflies (and the other pollinators attracted to the same plants) are hugely important to the ecosystem. Butterfly larvae are a major food source for birds and small mammals – some birds feed almost exclusively on caterpillars of a single species. Increasing local butterfly diversity and population will thus increase the local overall biodiversity and biomass, and sometimes dramatically. It doesn’t have quite the same ring, but I like to think of my garden as a “biodiversity garden.” Some call them “native plant gardens,” or a similar variant. whatever the term, the idea is to support the ecosystem by planting plants that have naturally evolved with other life in the area over millennia.
Designing a butterfly garden, as any garden, begins with deciding what you wish to plant. The goal here is to include mostly native plants that will attract butterflies (and moths and skippers – I probably should be saying “lepidopterans”). Butterflies rely on plants for food during both active stages of their life cycle: the adults feed on nectar and the caterpillars feed on leaves. Like humans, the young of butterflies can range from not picky (generalist) to extremely picky (specialist) eaters. The monarch is the classic example of a specialist – its caterpillars will only feed on milkweeds (Asclepias species). Plants a given species will eat are called “host plants” for the species, and females will only lay their eggs on suitable plants. Adults are typically much more cosmopolitan in their tastes, but feed on nectar. A successful butterfly garden will feature nectar plants to attract the butterflies and host plants to keep them there and propagate them. Of course, many plants serve both purposes, making them ideal choices.
There seems to be some debate regarding the ideal ratio of host plants to nectar plants. My beginner’s take is that it probably doesn’t matter much as long as both are present in significant quantities. However, the more limited the space the more selective one must be. I have hedged my bets a bit by planting as many plants as possible which fill both roles and building around those. Additionally, it’s helpful to consider what is planted elsewhere in your yard and immediate neighborhood. Butterflies after all will not recognize the boundaries of your garden or your property, so plants nearby can also contribute. Many trees and shrubs which may not be practical fits in your butterfly garden space are host plants for a diverse mixture of butterflies and moths. Most common oaks, for example, host hundreds of caterpillar species. Spicebush (Lindera benzoin) is a host plant for the appropriately named spicebush swallowtail. Viburnums host many species and produce lovely white flower clusters.
Aside from plants, a number of other things can encourage butterflies to visit your garden or extend their stay. Many butterflies will feed on overripe fruit, so a suspended tray of fruit can be a nice feature. Some feeders include a sponge soaked in sugary water as well. Butterflies also engage in a behavior called “puddling” to soak up nutrients from wet soil, and providing them with a space to do so can entice them to hang around longer. You can purchase a puddler or make your own, or simply rely on mud puddles. Butterfly houses can also be bought or built as encouragement for your visitors to hang around. Rock piles and/or log piles can serve a similar function (providing shelter from weather and predators). It’s also a good idea to add a place for humans to sit and observe the wildlife; I built a bench from (mostly) natural wood for this purpose.
Much of the source material I turned to when planning my butterfly garden focused pretty extensively on monarchs and milkweeds. It led me to wonder why monarchs in particular get so much of the butterfly press, but the more I think about it the more it makes sense. Monarchs are beautiful, large butterflies that are well known. Because of the viceroy, they’re part of the definitive example of Batesian mimicry. They are also in trouble because milkweeds are in trouble. As I’ve mentioned, their larvae will only eat milkweeds. As one might infer from the name, these plants have long been regarded as, well, weeds. People have been systematically removing milkweeds from a lot of areas, unwittingly endangering monarchs in the process. It isn’t just a problem for monarchs, though. The milkweed tussock moth, small and large milkweed bugs, red milkweed beetle, and other insects all rely heavily on Asclepias. The relationship between milkweeds and monarchs is a very illustrative example, but far from the only example. Adult butterflies will feed on the nectar of non-native flowers, but virtually no non-native plant can host a native caterpillar.
This returns me to the butterfly garden’s true purpose: to contribute ecological functions to the local biosphere. The native host and nectar plants have evolved relationships with many local forms of life on a grand time scale. Restoring these plants to an area also restores those relationships. Alien plants can stand in and provide some of the ecological functions, but not nearly all. I won’t advocate for the complete removal of all non-natives from gardens and other home landscaping, and I make concessions in this area myself. Increasing the number and variety of native plants in one’s yard, though, is a noble goal and a butterfly garden provides an excellent framework for doing so.