A milkweed by an other name …

What’s in a name? that which we call a rose
By any other name would smell as sweet;
– Juliet, Romeo and Juliet, Wiliam Shakespeare

A rose is a rose is a rose is a rose.
– Gertrude Stein, various

I started to get into a little tiffle on a post (since removed) on one of the insect ID groups in Facebook. The original poster was trying to ID a tight cluster of orange eggs on a leaf of a plant she identified as “milkweed vine.” One of the responders commented: “Milkweed vine? Not likely.” And then we were off.

What’s a “milkweed,” anyway?

Responding in a comment, the original poster specified that the plant was Morrenia odorata, an introduced, and invasive, vine in the Apocynaceae, the dogbane family. (Some authorities still list it under Asclepiadaceae, the milkweed family, which is now considered a sub-family, Asclepiadoideae, of Apocynaceae.) Its common names include latex plant, strangler vine, and, yes, milkweed vine.

The responder’s objection was that “Aclepias is milkweed.” Period. Final. Absolute declaration.

It’s not that simple.

Common names like “milkweed” have no authority. Many plants have “milkweed” as part of their common name, not just Asclepias species. Cynanchum laeve, a native vine in the same family as Morrenia and Asclepias, has a common name of climbing milkweed, among several others.

Noone can claim that only Asclepias species can be called “milkweed.” To insist so is, at best, dismissive. I would use stronger language. (I blocked the responder on Facebook to avoid future tiffles with them.)

Why plant ID matters for insect ID

Why did the original poster include the id of the plant in their requesting for identifying insect eggs? Because they understand that many insect species depend on different types of plants. Specialist insect-host associations are common in the co-evolutionary biochemical arms race between insect herbivores and their host plants.

Only five years ago, I didn’t have any knowledge of insect-host plant relationships. Marielle Anzelone (@NYCBotanist on Twitter – follow her!) clued me in on what was going on when I observed this in my backyard in May 2011:
Battus philenor, Pipevine Swallowtail
I recognized it as a swallowtail. Knowledge of the plant – Aristolochia tomentosa, wooly dutchman’s pipevine – id’d the butterfly as pipevine swallowtail, Papilo troilus. The caterpillars of this species feed only on plants in the Aristolochiaceae, the pipevine family, primarily – but not exclusively – Aristolochia species.

And so it is with “milkweeds” and their most famous herbivore, the caterpillars of monarch butterflies, Danaus plexippus.
Danaus plexxipus, Monarch, on Eupatoridelphus maculatus (Eupatorium maculatum), Spotted Joe Pye Weed
The butterflies nectar on a wide variety of flowers. Their caterpillars, however, are specialized feeders on plants in the Apocynaceae. While they are most commonly associated with Asclepias species, they have also been observed on Cynanchum and Apocynum species. They have even been observed on a few plants outside of this family.

So, when trying to identify insects, knowledge of plants, plant families, and their ecological associations is also important. Being pedantic about common names, not so much.

Related Content


Battus philenor, Pipevine Swallowtail, Butterflies and Moths of North America (BAMONA)
Battus philenor host plants, HOSTS: World’s Lepidopteran Hostplants Database
Danaus plexippus host plants, HOSTS: World’s Lepidopteran Hostplants Database
Aristolochia tomentosa Sims, woolly dutchman’s pipe, USDA PLANTS Database (Synonym: Isotrema tomentosa (Sims) Huber)
Isotrema tomentosum (Sims) H. Huber,  NY Flora Association Atlas (Does not list as present, let alone native, in NY)

Papilio polyxenes, Eastern Black Swallowtail

Update 2012-09-10: Only one caterpillar remains.

The morning of the day we left on our last road trip – which led us to the Adirondack Hudson, among other places – I saw this in one of our vegetable beds:
Papilio polyxenes, Eastern Black Swallowtail

This is a female Eastern Black Swallowtail Butterfly, Papilio polyxenes. I caught her at the moment she discovered our group of parsley plants (Petroselinum hortense, or P. crispum). She was laying eggs, carefully placing just one under separate leaves of two of the plants.

Papilio polyxenes, Eastern Black Swallowtail, ovipositing on Petroselinum hortense (P. crispum), Parsley

The eggs are tiny. For scale, my thumbnail is about 1/2″ wide.
Egg, Papilio polyxenes, Eastern Black Swallowtail

Eastern Blacks are members of a mimicry complex that includes several other species of large, black or dark brown swallowtails with spots and blue iridescence:

The beautiful Pipevine Swallowtail, Battus philenor, is the model of a Batesian mimicry complex. The members of this complex present a confusing array of blue-and-black butterflies in the summer months in the eastern United States. These include the Spicebush Swallowtail, Black Swallowtail (female), Tiger Swallowtail (dark phase, female), Red-spotted Purple and Diana Fritillary (female).

There is some indication that the Spicebush and Black Swallowtails are also distasteful, so the complex is partly Mullerian as well. In the central and western US, Old World Swallowtail (Papilio machaon, form bairdi), Indra Swallowtail (Papilio indra), and Ozark Swallowtail (Papilio joanae) have dark blue/black forms, probably mimics of the Pipevine Swallowtail.
– BugGuide: Battus philenor – Pipevine Swallowtail

Fortunately, several species in this complex have strong preferences for host plant families: Spicebush prefers Laureaceae, Pipevine prefers Aristolochiaceae. Knowing that the host plant, parsley, is in the Apiaceae, the Carrot/Dill Family, made it easy to quickly identify this butterfly, as the Black prefers plants in this family.

When we returned from vacation, the caterpillars had already hatched. Most of them were big! But some were still underdeveloped. I counted 14 overall.

Their appearance changes dramatically as they mature through each instar, or molting.

Early Instar Caterpillar, Papilio polyxenes, Eastern Black Swallowtail
Early Instar Caterpillar, Papilio polyxenes, Eastern Black Swallowtail
Middle Instar Caterpillar, Papilio polyxenes, Eastern Black Swallowtail
Mid Instar Caterpillar, Papilio polyxenes, Eastern Black Swallowtail
Late Instar Caterpillar, Papilio polyxenes, Eastern Black Swallowtail
Papilio polyxenes, Eastern Black Swallowtail

In the final stage, they are supposed to be mostly green. Several have reached that stage. I’m anxiously waiting for them to form chrysalises. And then, new butterflies! But probably not until next year, as they overwinter as chrysalises, and it’s getting late in the year.

If you have ever wondered how your vegetable plant could get denuded overnight, watch this video of one of the caterpillars feeding. The speed has not been modified, time-lapsed, or sped up. They eat fast!

Update, 2012-09-10

Most of the celery leaves are gone. The plants themselves have survived, and new leaves are emerging from their centers.

Their numbers gradually dwindled since I wrote this post. I couldn’t tell if they were leaving to seek a new food source, or to pupate.

By yesterday, only two large caterpillars remained. I observed one of them leave the plant and start to climb the frame of the raised bed. There was nothing for it where it was heading, so I moved it to part of one plant where leaves remained. It didn’t start feeding, as I expected. Instead, it took off in the opposite direction, toward the tomato plants.

A caterpillar of Papilio polyxenes, Eastern Black Swallowtail, on my hand

I intervened a second time. This time, I removed it to the backyard, where I’m growing Zizia aurea, a native plant in the Apiaceae, in a mixed border. Even if it wasn’t going to feed any more, there are more options of plants, including shrubs, for it to climb and pupate. The disadvantage is that the backyard is much shadier.

Only one caterpillar remains. Soon it will set out on its own, as well, and this adventure will be over, for this year.

My plan for next year is to move some of the Zizia to ground adjacent to the raised bed. I’m hoping both that the it will thrive in a sunnier location, and that the Swallowtails will prefer it as a host plant. We will see.


Related Content

Flickr photo set: Papilio polyxenes, Eastern Black Swallowtail
Gardening with the Lepidoptera, 2011-06-11



Gardening with the Lepidoptera

Tomorrow, Sunday, June 12, my garden will be opened for its second tour of the season: the Victorian Flatbush House (and Garden!) Tour, to benefit the Flatbush Development Corporation (FDC). Earlier this week, I wrote about the transformation of the garden over the six past years, since we bought our home. Today, I’m providing details about one part of that transformation, one which is easy to replicate on a small scale, even in a tree bed or on a balcony.

After readying my backyard native plant garden for its debut tour for NYC Wildflower Week in May, I decided to complete the requirements to register my garden as a Certified Wildlife Habitat (#141,173) with the National Wildlife Federation. With over 80 species of native plants, I easily met three of the four requirements: shelter, food, and places to raise young. All I lacked was water, a requirement satisfied by placing some birdbaths and a terra-cotta cistern.

On Friday, May 27, I mounted the plaque on the entrance arbor.
Certified Wildlife Habitat sign

The morning after I put out this welcome mat, I saw butterflies visiting a vine in the garden. I was puzzled, since the plant wasn’t blooming yet. Closer observation revealed that they were laying eggs on the vine.

Battus philenor, Pipevine Swallowtail
Battus philenor, Pipevine Swallowtail, ovipositing on Aristolochia tomentosa, Wooly Dutchman’s Pipevine

At first, I thought they were Papilo troilus, Spicebush Swallowtail, a species I’ve encountered before. But one of my tweeps, Marielle Anzelone, id’d it as Pipevine Swallowtail, a lifer butterfly for me. Upon researching the species, I was somewhat relieved to learn my confusion has some scientific basis: both the Spicebush and Pipevine Swallowtails, along with several other species, are members of a mimicry complex. As described on BugGuide, “members of this complex present a confusing array of blue-and-black butterflies in the summer months in the eastern United States.” The arc of orange spots on the underside of the hindwind, clearly visible in the photo above, is a key to distinguishing this species from other members of the complex.

The other key was the host plant. Of course, Pipevine Swallowtail would lays its eggs on Pipevine, in this case,  Aristolochia tomentosa, Wooly Dutchman’s Pipevine. This plant was a rare find; I’ve never seen it offered again, or elsewhere. A few years ago, I visited Gowanus Nursery – my favored retail source for native plants in Brooklyn, even New York City – and asked if they had any Dutchman’s Pipe. I was hoping for A. macrophylla, a species with huge leaves, and a Victorian gardener’s favorite. They had some Aristolochia, but neither of us could id the species. Adventurous gardener that I am, I took a chance and brought home a quart specimen with a few, thin stems and small leaves. When it eventually bloomed, I was able to id it.
Aristolochia tomentosa, Wooly Dutchman's Pipe

A few years later, the plant is huge, with dense foliage, though the leaves have remained small. It keeps reaching upward several feet, self-supporting its lax stems, and climbing into the cherry tree above it. It serves to screen the composting area from the rest of the garden. I think the mature growth of this plant, rather than the habitat plaque, is what attracted the butterflies to my garden, and select this plant as a host.

Eggs, Battus philenor, Pipevine Swallowtail
Eggs of Battus philenor, Pipevine Swallowtail on Aristolochia tomentosa, Wooly Dutchman’s Pipevine

Where I could find them, the eggs were laid only on the young leaves and petioles of fresh growth. This growth is abundant on the mature plant. The eggs are small, especially compared to the depth of the “hairs” of the plant. I suspect laying the eggs on young growth is critical to successful feeding by the young caterpillars. As they get larger, they can manage the larger, coarser hairs and leaves of more mature growth.
Empty eggs, Battus philenor, Pipevine Swallowtail
Empty eggs of Battus philenor, Pipevine Swallowtail, on Aristolochia tomentosa, Wooly Dutchman’s Pipevine. Leaf removed from the vine and U.S. quarter coin provided for scale.

Just five days later, on June 2, the eggs hatched. Newborn caterpillars!
Eggs and Hatchlings, Battus philenor, Pipevine Swallowtail

One day after they hatched, I found a group of four little caterpillars on the underside of a different, but nearby, leaf. Two days later, the group was down to three, and three days later, only two caterpillars were left on the leaf. The feeding damage visible in the photos is distinctive: other leaves on the vine have showed signs of feeding, or other uses, but nothing like the fine ragged edges left by tiny little mouths. I haven’t caught them in the act of feeding; I wonder if they feed at night, to avoid detection when active, and remain hidden during the day?
Caterpillars, Battus philenor, Pipevine Swallowtail
Caterpillars, +2 Days, Battus philenor, Pipevine Swallowtail
Caterpillars, three days after hatching

I’ve lost track of the caterpillars now. The vine is dense, with layers of foliage, and many twisting stems. I’ll watch for feeding damage to try to locate and photograph some of them again as they get larger. I’ll also look for chrysalises; catching them emerging as butterflies would be fantastic luck.

Aristolochia tomentosa is native to eastern and southern North America.
Map of native range of Aristolochia tomentosa

Battus philenor hosts on all species of the genus, so its range covers most of North America.
Battus philenor, Pipevine Swallowtail, Distribution Map, BAMONA

So, how is any of this “easy to replicate”? While flowers provide food to, and the plants shelter, adult butterflies and moths, a host plant meets three of the four habitat requirements: shelter, food, and a place to raise young. Most native plant species are known to host something. Both Butterflies and Moths of North America (BAMONA) and the international HOSTS Database from the Natural History Museum in London are online resources you can use to discover Lepidoptera-plant host associations.

A single container of a grass or sedge on a balcony can provide habitat. The whole of the cumulative impact of scores, hundreds of such micro-habitats will be greater than the sum. Even in urban settings, we can create opportunities for nature to return and thrive, and by reconnecting with it, we thrive as well.


Related Content

Battus philenor, Pipevine Swallowtail, Flickr photo set
Aristolochia tomentosa, Wooly Dutchman’s Pipevine, Flickr photo set


Battus philenor, Pipevine Swallowtail, BugGuide
Battus philenor, Pipevine Swallowtail, Butterflies and Moths of North America (BAMONA)
Battus philenor host plants, HOSTS: World’s Lepidopteran Hostplants Database

Aristolochia tomentosa Sims, woolly dutchman’s pipe, USDA PLANTS Database (Synonym: Isotrema tomentosa (Sims) Huber)
Isotrema tomentosum (Sims) H. Huber,  NY Flora Association Atlas (Does not list as present, let alone native, in NY)