Pipevine Swallowtails and the case for caterpillar gardening

When you think of gardening for pollinators, you most likely think of beautiful flowering plants which attract bees, butterflies, and other insects by offering copious amounts of nectar or pollen. But flowers cannot give all pollinators the food they need. Butterflies in particular can be very picky when deciding what to eat when first starting out their lives as caterpillars. Most butterfly species have evolved to specialize feeding on one or a handful host plants. In a sense, when it comes to supporting butterfly communities, providing ample host plants for these soon-to-be-butterflies could be just as beneficial as planting nectar flowers for adults!

Pipevine swallowtail eggs are laid in small clusters so that when they emerge, these caterpillars work together eating leaves in small groups

The Pipevine swallowtail Battus philenor is one butterfly that benefits tremendously from the gardening of its favorite plant, Pipevine Aristolochia, after which it is named. Both Pipevine and the butterfly with which it shares its name is native across eastern North America, including Massachusetts. The plant itself is highly toxic and could cause severe kidney problems or even cancer if ingested by humans, but Pipevine swallowtail caterpillars could not care less.

These caterpillars have evolved not only to cope with the toxins in the plants, but to actively seek them out. Pipevine swallowtails, like many other butterflies, including Monarchs and their beloved milkweed, acquire the toxic chemicals present in their host plant and sequester them. As caterpillars they build of reserves of this chemical making them unpalatable to potential predators for the rest of their life. This is part of the reason many butterflies display such bright and captivating scales – it can be a signal to predators that nothing good will come from eating them.

In the right conditions Pipevine can scale great heights clinging to trees or other supports

Though these caterpillars cannot get enough of Pipevine, the adult swallowtails themselves do not nectar on the flowers it produces. Pipevine, like the name suggests, produces curved flowers that resemble a smoking pipe which is not conducive for a butterfly proboscis. Dutchman’s pipe Aristolochia macrophylla, is the most common species in eastern North America, and produces small tubular flowers with a small circular entryway. Into that entryway go flies which are actually attracted to the flower’s fragrance. Upon entering the narrow pipe, the flies get a little stuck, catching some of the flower’s pollen and carrying it with them until they end up in another flower which they help fertilize. After fertilization, the plant produces great seed pods which, when rooted and grown, will provide more food for those hungry caterpillars.

Before you start thinking this toxic, fly-attracting plant might not be the right fit for your garden, consider that Pipevine has been an immensely popular ornamental plant since Victorian times. It is an ideal option for trellises, fences or pergolas, providing plenty of shade when mature! If you are interested in attracting these beautiful butterflies to your home or garden in the future be sure to water your Pipevine as it needs lots of water and give it a place to climb. Be sure, too, to get Aristolochia macrophylla specifically, as some species will not support these caterpillars or might even be invasive – moreover macrophylla will provide the best shade (it is given the Greek name meaning ‘large leaf’) and will attract some marvelous butterflies looking for the right place to lay their eggs.

Adult Pipevine swallowtails have a remarkable coloration, with black and iridescent blue wings that have orange and white spots on the underside (Photo credit: John Flannery)

Plants and pollinators in our gardens

Over the past few months, TPI members have hard at work sifting through and analyzing the data we collected in summer 2020. Each week, three times per week, we identified the flowering plants in our gardens and counted flower-visiting insects. We’ve summarized the diversity of plants and insects found in our gardens on two new webpages: Plant Diversity and Pollinator Diversity. In short…

Our gardens contain more than 20 species each of native wildflowers. At least one species was blooming in our gardens each week between May and October. Some of the most popular native wildflowers of pollinators and humans alike are wild bergamot (Monarda fistulosa), culver’s root (Veronicastrum virginicum), blazing star (Liatris scariosa), new york ironweed (Vernonia noveboracensis), and new england aster (Symphyotrichum novae-angliae). Do you have any of these plants in your garden?

Our urban garden is attractive to both people and pollinators!

Our gardens attracted over 115 species of insect pollinators. Some of those insects found food in our gardens: six different bumble bee species (Bombus spp.) collected pollen from sunflowers, sand wasps (Bembix americana) hunted flies, and gray hairstreak caterpillars (Strymon melinus) browsed on mountain mint. Other insects made their home in our gardens: furrow bees (Halictus sp.) and leaf-cutter bees (Megachile sp.) nested in the bare soils. Our gardens are just two years old and already they are supporting more insects than we could have imagined! We can’t wait to see what we find during our surveys in 2021.

Monarch butterflies refueled on goldenrod (Solidago spp.) in our gardens as they headed south to their wintering grounds in Mexico.

TPI spreading across Tufts campuses!

Early last spring, TPI was officially funded by the Tufts Green Fund. Since last year, we planted three pollinator gardens on the Medford/Somerville campus, and generated outreach materials for events on and off campus. Through live-facing events alone, TPI reached over 1,000 people in Massachusetts and Rhode Island!

For this cycle of the Green Fund, the Sustainability Committee from the School of the Museum of Fine Arts (SMFA) at Tufts University reached out about applying to fund pollinator gardens on their campus. As of yesterday, the SMFA pollinator garden project was funded!

We extend our congratulations and are excited to collaborate! Some of the seedlings we’re growing in the greenhouse, as well as TPI signs, will find a home in Boston later this year. If you see a pollinator garden while strolling the SMFA campus, take a moment to watch. You might be surprised by how many pollinators you see!