‘gardening for butterflies,’ with the xerces society
SUCCESSFUL ‘BUTTERFLY GARDENING’ is a more complex matter than bringing home a few so-labeled “butterfly plants” from the garden center that promise to do the job. Now there’s expert help in the form of a new book:
Matthew Shepherd is co-author of the Xerces Society’s just-published “Gardening for Butterflies,” and has been with Xerces since 1999. He has coauthored other Society publications, including their “Pollinator Conservation Handbook.”
Matthew is also a fellow gardener with an interest in creating gardens that provide for insects and other wildlife.
On the May 23, 2016 edition of my public-radio show, Matthew Shepherd took me through the life stages of butterflies. We talked about what they eat at each phase–like how important certain trees are in the dietary equation, why we should stop weeding out or even plant important native thistles, and how showy tropical milkweed and “butterfly bush” aren’t helping—and are actually hurting. Read along as you listen using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
my butterfly q&a with matthew shepherd
Q. The first butterfly to flutter through my garden this spring, as ever, was the cabbage white, maybe not my favorite since it spells potential trouble in the cabbage patch…but quickly came the charming little blue spring azure, and the bigger mourning cloak, and I even saw a very early tiger swallowtail in April.
But seeing butterflies doesn’t mean all is OK, does it? I thought we could do a quick scene-setter on why butterflies are in trouble, and why we want to care about gardening for butterflies?
A. Butterflies are one of those insects that at first glance seem to be everywhere. You mentioned the cabbage white, which seems to crop up early in the year, and there are enough of them around to be potentially a pest.
Often we don’t stop and think of the state of the butterfly, or the health of them. But there is an increasing amount of evidence that not only the rare butterflies—those species that mainly live on a mountaintop, or on some distant prairie—but those butterflies we expect to see in our garden, ones that fly across our neighborhoods, are actually beginning to decline. There are fewer and fewer of them. But often we don’t notice because we still see them, and we haven’t stopped to think. But we’re just seeing fewer of them, or it will be a week between sightings, for example.
So there are lots of things that are affecting this. One of them is just that these days we have ever-greater capacity to change our landscape. There’s the classic image of the bulldozer, and that’s what happening. New houses are going up; new businesses are needing factories and big box stores and all the other things we like to have around us as part of the convenience of our lives.
So the habitats are disappearing; the landscape is changing.
Q. And of course we have as a culture used chemicals for agriculture and other reasons that have impacted on many insects and other organisms.
A. Large areas of our landscapes are cultivated, are farmed. Those areas are inhospitable—they might look green, but there is not much out there to support a butterfly.
Q. One of the things people may not know is the life cycle of a butterfly.
A. The basic life cycle is the same for all butterflies. There’s an egg, and then the egg hatches into the caterpillar, and the caterpillar grows and actually goes through a number of stages, which are known as instars.
They can’t grow outside of their skin, so they have to molt. Each time they molt they become another instar, and get bigger and bigger.
It’s remarkable how quickly a caterpillar will grow. A monarch caterpillar, for example, in a matter of only a few weeks—we’re trying to work this out, how many times bigger it is at the end, when it’s big enough and about to pupate. It’s thousands of times bigger from when it comes out of that tiny little speck of an egg.
So the third stage in the life cycle is the chrysalis, when this little worm/grub-like chewing, plant-eating caterpillar disappears for awhile and it returns with wings, and it flies, and it drinks nectar, and it’s totally transformed. And then there’s the adult, which we often see as the butterfly—the adult is the fourth stage.
Different species need different things to complete this life cycle. One of the key components is the right kind of plants for the caterpillar to eat. It might vary from the monarch butterfly caterpillar, which eats milkweed, through a small skipper butterfly that eats grasses. There are many that will eat oak trees or willow trees or many different plants. [Above photo, black swallowtail caterpillar in Margaret’s garden.]
Q. You mentioned milkweeds, and that’s an interesting thing because not all milkweeds are created equal—and that’s true of all these plants you’re alluding to. It isn’t just any milkweed that is going to support a particular butterfly, right?
A. That’s right. There are several-dozen species of milkweeds that are native to North America. In the Midwest and the Great Plains, some of the species such as the bright orange-flowered one often called butterfly milkweed [Asclepias tuberosa] and then the pink-flowered common milkweed [Asclepias syriaca] and swamp milkweed [Asclepias incarnata].
Some of them are probably better for supporting monarchs—a bit more palatable for the caterpillar. As many listeners probably realize, milkweed is toxic in itself. There are a lot of things that won’t eat it, but the monarch caterpillars have a remarkable ability to overcome the toxins. In fact they absorb them into their own body, which makes them taste bad. That’s why they’re brightly colored—they don’t have to hide; they can be yellow and black with white stripes, because birds will quickly learn that you don’t eat one, because it tastes disgusting.
There is more of an issue in the Southern states, because there is one species called tropical milkweed that’s very popular with gardeners. It’s easy to grow and is available in a lot of garden centers
Q. That’s Asclepias curassavica, I think? [Photo above from the book, by Forest and Kim Starr.]
A. Right. But because it’s an evergreen, it means that now there are periods of the year when typically the native milkweeds would die away and disappear, but now you’ve got this evergreen species. It is allowing monarchs in some places to be breeding for longer. And also because the plant doesn’t die away, there is unfortunately a parasite that is affecting monarch caterpillars. What that means is that the caterpillar will complete its growth and will pupate—it will become the chrysalis—but it won’t complete metamorphosis, and won’t ever appear as an adult.
So that’s a problem that seems to be associated with the tropical milkweed because it grows all year and allows the caterpillars to pick up the spores from this parasite.
Q. It’s interesting because if one went to the garden center—or I kind of remember when I first saw tropical milkweed in catalogs a number of years ago touted as a butterfly plant. But here we are and it backfires, and proves harmful—confusing their natural course of events and their life cycle, and interrupting things. It’s not sustenance, after all, but can short-circuit things.
A. It’s a great shame because it will actually allow monarchs to grow. Sometimes these milkweeds will be growing where there aren’t any others, so the monarchs are able to use them. But it’s proving to be an unfortunate threat to those butterflies that feed on it.
Q. Speaking of things where you see a picture in a catalog and it says, “butterfly bush”—that’s another one where I don’t think any native species of butterfly can actually live off that plant through all their life phases.
A. I think you’re right. Often non-native plants don’t support the same range of species. Certainly when it comes down to caterpillars needing something to eat, native species tend to have co-evolved with other native species. So native plants are better for feeding native caterpillars, whether it’s a moth or a butterfly. And the butterfly bush, Buddleia davidii in particular, which is often called the orange-eye butterfly bush I think, is actually an invasive species, and in the wrong places it will spread dramatically.
Q. Yes, it does.
A. That’s its main threat, and in fact there are some states—Oregon is one of the states—where it’s on the official noxious weed list and you shouldn’t be planting it.
Q. And again: Even if you’re not in Oregon, it’s not all that they need—it doesn’t have that intimate co-evolved relationship like some other plants. I guess what we’re getting to is that if we want to do our best job “Gardening for Butterflies”—the title of the new book—probably we want to look at our native species that support these creatures.
A. And that’s the underlying message of the book. All the way through the book, the plants that we talk about are native. In particular one of the major benefits of native plants is providing food for the caterpillars. Caterpillars in themselves are a food source for most species of birds in North America—particularly songbirds, and for feeding their young while they’re in the nest. Caterpillars are these fantastic little protein bullets.
Q. And they’re kind of squishy, too. [Laughter.]
A. They are. We talk about superfoods—the latest superfood fad, whether it’s a vegetable or a berry. Caterpillars are superfoods for the birds. Dr. Doug Tallamy at the University of Delaware has for year been looking at which caterpillars are eating which plants, and their work has shown that on average, native species of trees and shrubs support 74 species of native caterpillars, and non-native trees and shrubs only support five.
Q. Seventy-four compared to five? It’s not even close, is it?
A. It’s dramatic. That work does underscore the importance of having the right plants to support the butterflies and moths when they’re at the larval stage, as caterpillars.
Q. Among other plants: A lot of gardeners are obsessed with weeding out thistle. Thistle is a word that conjures “weed,” and then there are thistles that have been touted as an ornamental because they have showy foliage, or they’re statuesque, or have a big seedhead—whatever trait. But a thistle is not a thistle is not a thistle—are there good and bad thistles if you’re a butterfly? [Above, pasture thistle photo from the book, by Frank Mayfield.]
A. From the perspective of the butterfly, they may all be good—but from the perspective of the gardener, or the farmer, there are some that are bad.
Thistles are a fantastic source of nectar. Some of the studies being done at the moment looking at plants that support monarch butterflies migrating south in the fall—it’s looking like thistle is one of the key nectar sources that are fueling those butterflies on their flight.
There are also thistles that are host plants. The caterpillars of some species use them, such as painted lady, the Mylitta crescent, and the California crescent. These are the some of the key plants for their caterpillars to feed on.
Unfortunately thistles have all been tarred with the same brush—these non-native species, like Canada thistle. It’s not a slight against our northern neighbors [Cirsium arvense is a European native]; for some reason that’s the name it’s been given. That’s one that really is a problem species and should be controlled, whereas unfortunately our native species such as pasture thistle [Cirsium discolor] or the tall thistle [Cirsium altissimum] have just all been controlled and eradicated as well.
Q. So that’s a plant where when we look at it as a gardener, and say, “Weed status,” maybe we should think instead, “Wait a minute; maybe this has tremendous value.”
I think goldfinches use the sort of floss to make nests, too.
A. And it’s not just the nesting floss, but the seeds that help the birds fatten up and get ready for winter.
Q. Right; they wait for that, to breed. So we’re putting a gold star next to some thistles.
There was a section in the book about the importance of trees, and again I think a lot of people coming at this as gardeners—from reading catalogs, or going to garden centers—see things labeled “butterfly plants,” but they’re not trees, typically, that are labeled that way. I’m thinking, “I’ve got to get this milkweed,” and “I’ve got to get this butterfly bush.”
A. A lot of the plants are labeled “butterfly plants” because they’re nectar plants. Most garden centers aren’t selling plants that are going to get chewed on and look ratty after awhile.
A. Providing the nectar for the butterflies is easy. It’s providing for the rest of their life cycle that requires thought. And often we’re not looking up above our heads. You might have an oak tree in your garden. My garden’s not big enough to have an oak tree; I wouldn’t have any garden if I had a mature oak.
But if you do have one, keep it; it’s a fantastic tree. It’s one of the trees that supports the greatest number of insects in its entire life. Literally hundreds of different species. There are some butterflies that rely entirely on the oak for their caterpillars to eat, so it really is a fantastic tree to have. But maybe you have a smaller garden and don’t have room for an oak tree, so there are some of the smaller trees—the willows, for example, are another great plant.
Q. And with willows, another great thing is that they often flower very early—and I think extending that sustenance, even if it’s just from the flowers. It’s pretty great to support early insect pollinators of all kinds.
A. With willows, it’s some of the early emerging mining bees and bumblebees. By putting a willow tree into your garden, it’s becoming much more than just a butterfly garden.
Q. And wild cherry trees–I was interested to see that was another one that was on the recommended list.
A. The chokecherry [Prunus virginiana] is one—it probably supports more moth species at the caterpillar stage than butterflies, but moths are just as important to keep in our environments.
Q. You said the “M” word—I have a thing for moths. [Laughter.] I was so glad that the book “Gardening for Butterflies” included moths, who I think are sort of their overlooked cousins, and it’s a shame. First of all, many of them are at least as spectacular as any butterfly. [Above, a few of the moth’s in Margaret’s garden, clockwise from top left: clymene, luna, small tolype, cecropia.]
A. Oh, yes.
Q. You also include all the groups—in field guides, there may be separation, a section about the butterflies; a section about the skippers; a section about the moths. Understanding them all—the book encourages us to do that, and to provide for them all.
A. You can’t really separate them out in your garden.
Q. Not at all.
A. So if you’re thinking about which plants should you be planting to provide nectar, or feed the caterpillars, the chances are they are the same, anyway. So by making a good garden for butterflies, you’re almost inherently creating a good garden for moths.
What it does is give you a greater opportunity to get out. I’m at work all day—I don’t get to sit in my garden at the hot part of the day watching the butterflies. But when I’m there in the evening, that’s when I encounter the moths—or when I step outside to pick the newspaper up from the driveway, there are the moths on the wall underneath my porch light. It’s an insight into a different world.
Q. Speaking of the things that butterflies eat, and their caterpillars eat, there’s a photo in the book…
Q. I don’t even have to tell you what it is and you are laughing.
A. I know which one: It’s the one on coyote scat. [Photo above from the book, by Bryan E. Reynolds.]
Q. Coyote scat. There are like six different species of butterflies having a feast.
A. Butterflies are this little fragile image of beauty we have when in fact some of them have really nasty habits. [Laughter.] Most of the butterflies that are feeding on other things are often males, which are gathering the protein and little amino acids that strengthen them so they will be able to breed.
They’re gathering these nutrients from mud puddles and they get them from scat, and sometimes you even find them on carcasses—roadkill and such things. So it’s pretty nasty. You go along and there is this stunningly beautiful animal sitting on top of this really nasty thing. [Laughter.]
Q. I know regional issues are a challenge with this next question. But when choosing plants for butterfly support, you’re urging us to use natives, and to look at the different moments in the creature’s life. Any other guidance?
A. Those are the key things. If you’re going to create a butterfly garden, one of the first things to do is try to figure out what butterflies you have in your area—and there are fields guide that can do that, and websites.
And also just keep your eyes open and be looking to see what you can find, because you may suddenly realize that there’s a patch around the corner from you that supports a few butterflies, or a few caterpillars, and it gives you a chance to see what they’re already living on in your area.
I’ve already said my garden is too small for an oak tree, but I know there are oak trees growing a few houses from me, and there are willow trees on the long side of a little creek a block and a half away. So in my neighborhood, some of those things are already there, but what’s not?
That gives me a chance to focus my gardening on what’s missing from the neighborhood, in order to complete the life cycle.
more help from xerces society
- The Xerces website
- The Xerces milkweed FAQ page
- The Xerces pollinator-friendly plant lists by region
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the May 23, 2016 show right here. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
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