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)

Let herbs flower in your quarantine garden

As the heat of summer approaches, your quarantine garden will rely on insect pollinators to produce its bounty. Tomatoes. Cucumbers. Heaps of zucchini. This free ecosystem service—pollination—is often taken for granted, but it wouldn’t be possible without the help of insects: bees, butterflies, hover flies, beetles, and wasps.

To support these insect pollinators, you don’t need another garden. Simply let your herbs flower.

Herbs are a group of plants that have at least one organ (leaves, stems roots, flowers) that is tasty or medicinal. Leaves and stems get all the attention, while flowers often get overlooked, clipped away with the dead leaves and added to the compost. Not only are herb flowers almost always edible, but they also offer a veritable feast—nectar and pollen—to pollinators.

herb flowers
We most often eat the leaves and stems of herbs, like chives, thyme, and sage, but pollinators feast on the nectar and pollen from the flowers. PC: Timothy Vollmer, Flickr

Case in point: chive flowers feed sweat bees and carpenter bees after a long winter; the inverted flowering parasols of dill are a favorite of beneficial wasps and hover flies; and you’d be hard-pressed to find a flowering blade of lavender without a bumble bee. Moreover, flowering herbs teach a valuable lesson in pollinator gardening 101. Diversity begets diversity. To support all the pollinators that make your garden productive, plant diverse herbs.

Bumble bees are always attracted to the nectar-laden flowers of oregano. PC: Nick Dorian

It’s not hard to get started. Compared to pollinator-friendly native plants*, herbs are easy to procure. Seedlings are available for purchase at garden centers and many grocery stores in spring and summer.  

Herbs are also conducive to being grown in containers, making pollinator gardening possible anywhere, even on balconies or in window boxes. Herbs are forgiving to grow (sometimes downright invasive, another reason to use a container) and only require regular watering and some direct sun. And best of all? The strong flavor of the leaves that we enjoy in our cooking is despised by rabbits and deer.

Herbs are particularly conducive to container gardening. Here, the gardener has flanked orange tomatoes (center) with herbs. By letting their herbs flower, they will support bees that pollinate tomatoes. PC: greckor, Flickr

When picking out herbs for your garden, my recommendation may seem counter-intuitive: grow what you like to eat. Gardening for pollinators can be more involved, but it doesn’t have to be. All flowering herbs support pollinators. By selecting particular combinations of herbs to grow, however, you can maximize the benefits of your quarantine garden for pollinators. Here are four tips:

  1. Combine herbs that vary in flower shape (e.g., dill, lavender, borage, chamomile).
  2. Combine herbs that vary in fragrance (e.g, cilantro, basil, rosemary, lemon balm).
  3. Combine herbs that vary in size (e.g., thyme, chives, nasturtium, fennel).
  4. Combine herbs that flower in succession, from spring (e.g., chives, sage, rosemary) to early-summer (e.g. thyme, lavender) to late-summer (e.g., basil, oregano).

Next, put your herbs in the ground or in a pot with plenty of room to grow (6-8” between plants). Water them well at first, then a few times per week or whenever the leaves begin to wilt. If you already have herbs in your garden, even better! You’re ahead of the game.

In New England, thyme flowers in early summer and feeds many pollinators. It’s perennial, meaning it will feed pollinators year after year. PC: Nick Dorian

Harvest leaves and stems throughout the season (morning or early evening is best!). Use them fresh or dry them for later. A few of my favorite things to make with herbs: mint-watermelon cooler,  gnocchi with brown butter-sage sauce, and pesto potato salad.** With leftover pesto, I make pesto ice cubes to enjoy garden freshness all winter long.   

At some point during the growing season, your herbs will want to flower. The flowering time of the herb depends on its life cycle. For perennial herbs that come back each year, such as chives or sage, the plant will flower at a predictable time each year alongside your harvest. For annual herbs that die at the end of the growing season, such as basil or cilantro, the plant will flower at the end of summer or if it gets too cramped in its container. In both cases, the leaves and stems are still edible while the plant is flowering, but they will be tougher and less sweet than before.***

Honey bees love flowering lavender!

Letting your herbs flower is a simple, intentional act that sets in motion the dinnertime rush. Take time to notice your guests. Notice how bees push and reach over each other to get food on their plates, family style. How hover flies wait back for the perfect moment to land, so they can eat without being disturbed. How butterflies sip nectar, polite and upright, as if dining at a fine restaurant. Take pride that you’ve put food on their table, just as they have on yours.

*Flowering herbs are non-native, introduced by colonists. That means our native pollinators don’t share an evolutionary history with herbs and, therefore, don’t benefit as much from herbs as they do from native plants. If you’re interested in adding native plants to your garden, check out our handout for recommendations on what to plant.

**Pesto potato salad

  • 2 cups quartered baby potatoes
  • 1T paprika
  • 2T chopped rosemary
  • 1c green beans, cleaned and cut into 1in pieces
  • 4 roma tomatoes, halved
  • 2c fresh basil, loosely packed
  • 2T sunflower seeds
  • juice of half a lemon
  • 1/4c grated parmagiano regiano
  • 1/2c extra virgin olive oil + 2T extra for potatoes
  • 1 large or 2 small cloves garlic
  • salt and pepper to taste

Preheat oven to 400˚F. Toss quartered potatoes in olive oil, salt, pepper, paprika, and chopped rosemary and roast in oven for 35-40 minutes. Meanwhile, blanch green beans in boiling water for 60 seconds, then shock immediately in ice water. Set aside. If possible, grill tomato halves for 8 minutes, until charred and cooked. If not, place in the oven with potatoes for the final 10 minutes of roasting. Dice tomatoes and toss the body of the salad to mix. Dress with pesto (see below). Enjoy!

Earlier that same day (or while potatoes are roasting), prepare pesto. Process together basil, sunflower seeds, lemon juice, garlic, cheese, and s&p, slowly drizzling olive oil into the blender to emulsify and incorporate. Adjust seasoning to taste. 

***Nick’s tip: If you want to delay the flowering of your herbs, perennial or annual, clip off incipient flower buds. Do this when the buds are small.