WHAT ARE INSECTS THINKING–or if that sounds like I’m anthropomorphizing, what at least are insects desiring? The more we humans seek pollinator connections in our gardens, and strive to create a piece of habitat and not just a purely pretty backyard, the more we want to get inside their heads and understand their cravings, right?
I have the pleasure of interviewing entomologists and ecologists pretty regularly on my public radio program and podcast, and in 2018 a few conversations touched on my question about what insects are after.
The year ends in my northern garden with outdoor insect activity at its low point, but I’ve nevertheless been thinking of them, and of some key takeaways from interviews this past year about “the little things that run the world,” as Harvard biologist Edward O. Wilson famously called insects and other invertebrates. I rounded up some of what I learned about insects in 2018.
Read along as you listen to the Dec. 31, 2018 edition of my show and podcast using the player just below the next photo. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
WHAT ARE FIREFLIES thinking about with all that flashing on summer nights? Apparently firefly experts have various views on the many factors involved in this signature behavior, but I got a streamlined answer from Lynn Frierson Faust, author of the recent field guide “Fireflies, Glow-worms, and Lightning Bugs” from University of Georgia Press. (Our entire interview is here.)
All the experts, including Lynn, agree on a couple of things: It’s male fireflies who fly around flashing, and what they are thinking is about a hookup. And they especially agree that it’s hard to get your flashing seen by a female with the massive amounts of outdoor nighttime light pollution we humans have created.
Here’s how she explains what’s going on:
Lynn Frierson Faust. “There again, you get a bunch of firefly people together and they’ll have 50 different reasons, and we do think it’s actually multiple reasons. In the world now, it’s primarily for mating, and it’s a love song that the male sings through light to try to attract the female to answer back. The females are usually hidden down in the leaves, and he’s the one you see at night.
When you’re a little girl chasing them in your yard or your grandmother’s yard, it’s the males that fly around. They’re flashy, they want to be seen, and each species has its own specific little pattern it does that only his female will recognize. And when one of them catches the female’s eyes, she will bend her little abdomen and she usually just has a little light, a little tiny lantern, and she will aim it at the male she wants, and flash, and hopefully he sees her and lands, and they mate.
But that is where light pollution comes in, it’s devastating, because no firefly can compete against a glaring outdoor light. So it’s their song of love.”
I HAD NEVER KNOWN that each firefly species had a particular, carefully timed pattern of flashes–like its own unique Morse code pulsed in light, its own language to others of its kind. Brilliant, literally.
In a couple of the year’s segments I was also reminded by my guest experts of this reality: that to bees and butterflies and others, bigger isn’t always better. Though we gardeners may gravitate toward the high-drama, double-flowered version of some perennial or blooming shrub, such overblown choices often get a resounding thumbs-down from pollinators.
George Coombs, who was recently promoted from Trial Gardens Manager to Director of Horticulture at Mt. Cuba native plant research center in Delaware–congratulations George!–mentioned this when we spoke about a trial he had conducted to compare cultivars of garden phlox, Phlox paniculata, a beloved butterfly plant. Here’s George, after I asked him what besides their degree of resistance to powdery mildew disease he wanted to learn from the phlox trial:
George Coombs. “So we’re always interested in how these plants perform in the garden but being Mt. Cuba, focusing on native plants, we want to know well what do these plants do in the environment besides just being pretty.
George. So the thing that we were looking at with the Phlox trial is we wanted to see what differences there were in their ability to attract pollinators. So we actually had a graduate student as well as some volunteers here at the garden to keep track of that.
What we found is that one cultivar in particular really attracted the most butterflies out of all of the sun-loving phlox types and that was Phlox paniculata ‘Jeana’ [above]. The really interesting thing is that that was also the top performer horticulturally, in terms of what blooms the most, is the most disease-resistant, etc., so that was a really nice coincidence. What they found is that even though this is the one that’s attracting the most butterflies, we’re not really quite sure what characteristics about ‘Jeana’ are bringing the butterflies in.
So the interesting thing about ‘Jeana’ is that its flowers are actually the smallest out of any of the flower sizes of garden phlox. They’re about the size of maybe, somewhere between the size of a pea and a dime. They’re quite smaller than normal, which you would think maybe an atypical flower size might deter butterfly visitation because they’re not necessarily used to seeing that. But for whatever reason that’s what they love. So the going theory is that well maybe that smaller flower size somehow makes it easier or faster for them to move between different flowers and visit and get more nectar quicker and easier.”
IN 2018 I ALSO ASKED Doug Tallamy of the University of Delaware, author of “Bringing Nature Home,” for any general insight into how cultivars of native plants compare from an insect’s point of view to the straight species that nature created. His answer from our chat speaks to differences not just in flower size, but also traits like showier leaf color or variegation that a breeder may have selected a plant for, in hopes it would appeal to gardeners.
The University of Delaware collaborates with George Coombs and Mt. Cuba Center, and in fact Mt. Cuba funded some of the university’s study of cultivars–including a recent undergraduate’s senior thesis on hydrangeas, particularly of the native species Hydrangea arborescens. (That’s the unadulterated species of wild hydrangea above, in a photo from Mt. Cuba.) Most of us only know one variety of that: the ubiquitous ‘Annabelle.’
Who knew this super-popular flowering shrub gets such bad reviews from pollinators? Here’s Doug Tallamy:
Doug Tallamy. “If you go to the store and ask for arborescens, they give you Hydrangea arborescens ‘Annabelle.’
Margaret. ‘Annabelle,’ sure. [Laughter.]
Doug. Because they’ve changed the lacecap flower into a mophead flower that is loaded with sterile bracts and that’s what the big mophead is—it’s all these white bracts. So no surprise, what the student did was set up video cameras and look at the flower visitors that came into the flowers. And ‘Annabelle’ was the bottom of the list.
Doug. Because first of all, it has far fewer fertile flowers, and even the fertile flowers it does have are very low in nectar. The nectar quality is very poor—so we’ve changed it. It’s prettier for us, but you’ve taken a native plant, which actually is a really great pollinator plant when it’s the straight species, and we’ve created a cultivar that’s almost useless to pollinators.
And that’s what people have to realize. What has a cultivar change actually done to your particular plant? There’s no one answer to that. The answer is: It depends.
If you have a double flower, those are all sterile. If you have anything that’s really, really showy, be suspicious that energy has gone into enlarging the bracts or changing the color, and it takes energy away from pollen and nectar production. And if you’re planting this plant for pollinators, you do need to know that.”
AND AS I MENTIONED earlier, it’s not just about the tinkering with flowers that can cause popular species of plants to be not so popular with pollinators and other beneficial insects.It’s even unusual leaf forms that can backfire. Here’s Doug Tallamy again, after I asked him whether all cultivars are less appealing, or if we can draw any such general conclusions like that:
Doug Tallamy. “You know that is the most common question I get. Are cultivars of native plants, and people just call them nativars—although I have learned the horticultural trade does not like that term-
Margaret. Oops. Too bad.
Doug. … but are they as good in terms of performing their ecological functions as the straight species from which they were derived?
Doug. It’s a good question, because when you go to the nursery, most of the time, that’s what’s for sale. It’s some genetic variant of a straight species. Now there are lots of reasons that cultivars are created, most of them do focus on aesthetics, but any genetic variant that is disease-resistant is also a cultivar.
Doug. Let’s make sure we’re not talking about hybrids. Hybrids are the cross between two different species, and they are offered as well, but it’s not officially a cultivar.
We just finished a study looking at six common cultivar traits in native plants, and seeing how they might have impacted insect use of that plant. Now these are all woody plants, so we did not look at flowering; we did not look at flowers at all. So we didn’t look at the impact on pollinators; other people are doing that.
But just in terms of how well leaves support caterpillars and other things that drive food webs. We looked at what happens when you make a green leaf, red or purple. What happens when you change that leaf into a variegated form? What happens when you take a tall plant and make it short, or change the habit in some way? When you enhance fall color? When you increase fruit size? What was the other trait? I think that’s it; there were six traits.
The only thing that consistently deterred insect feeding was taking a green leaf and making it red or purple.
Margaret. I knew you were going to say that and that makes me sad, but O.K. [Laughter.]
Doug. Yes. It makes sense because that’s changing the leaf chemistry.
Margaret. Of course. The chemistry and chlorophyll tastes different from what, the anthocyanin pigments, or something?
Doug. That’s right; anthocyanins are feeding deterrents.
Doug. So when you load a leaf with feeding deterrents, of course it deters feeding. [Laughter.] You know that is something that gardeners have been seeking for a long time. They don’t want any insects in their garden. And if our gardens just occupied a little space on this planet, that’d be O.K.
But they don’t, they occupy a huge area. It’s not just our gardens, all the landscapes around us. So not only do we bring in cultivars of native plants, we bring in non-native plants that are also very poor at supporting insects, and then a lot of those escape.
What is it?—85 percent of our woody invasive plants are from our gardens. There are very few habitats that aren’t just choked with plants, typically from Asia. So we’ve converted an awful lot of our land into a landscape with non-native plants that are not supporting the food webs that everything else needs.”
NOW, DOUG TALLAMY doesn’t expect us all to start over from scratch, to rip out everything and begin again, but does want gardeners to make more conscious choices in favor of natives and also to have all the facts when they shop for plants. He wants us to get better informed by using searchable databases like the one University of Delaware and National Wildlife Federation and U.S. Forest Service created recently, where you enter your Zip Code and get plant suggestions matched to your location. (Some other such sources are named in this earlier interview.)
Doug wants us to identify the really powerhouse plants we can add to our landscapes—the plants that support food webs. For instance, he says, an oak is the most powerful plant you can add in terms of wildlife species it supports. To support specialized pollinators, native willows, and goldenrods, sunflowers, and asters are the top ones, he says.
We need to do our homework, and select plants wisely. He made a couple of other important points, again about those cultivars of native plants, in our conversation:
Doug Tallamy. “There are two reasons that I wouldn’t turn to a cultivar as a first choice. One is that most of them are propagated clonally, which means there’s zero genetic variability. In the age of climate change, in particular—we’ve always needed a lot of genetic variability in our plants, but in the age of climate change, it’s particularly important. We’ve got all these wild swings. And putting plants with no genetic variability out in the environment is just not a good idea.
The other thing that bothers me, is if the only thing that we sell in nurseries are designed for aesthetics only, it perpetuates the idea that plants are just decorations.
Doug. Of course, they are decorations, and they are beautiful, and we do want beautiful plants in our yard. But we also want to think about those vital functions that they must be performing in our yard.
So I would just love to see straight species sold right along with those cultivars, so if the homeowner is more interested in restoration or getting the maximum value out of that particular species, they have the option of buying it. That’s what I would like to see.”
SO I’VE BEEN TALKING throughout this article about welcoming more insects, but let’s backtrack and ask this:
Do you know exactly what makes an animal an insect, anyhow?
In one of the most invigorating conversations of 2018, I had the privilege to talk to Dr. Michael Engel, the author of “Innumerable Insects: The Story of the Most Diverse and Myriad Animals on Earth,” lavishly illustrated with historic prints from the American Museum of Natural History Library collection. Engel is a research affiliate at the museum, and also a Professor of Ecology and Evolutionary Biology and Senior Curator of Entomology at the University of Kansas.
Until I read his book and spoke to him, I knew that insects have six legs…but not much more. What does an animal have to do, besides have six legs, to be an insect, I asked? Here’s part of what I learned from Michael Engel:
Michael Engel. “Well, that’s a good question. As a matter of fact, it’s clearly not just six legs, because there are other arthropods that have six legs that are not insects. So insects belong to this larger group called the Hexapoda, which is aptly named, meaning six feet. So the hexapods all have six legs, and they include some rather unfamiliar little things like springtails and so forth, and then the true insects. So what is it that makes, if it’s not just the six legs, what is it that makes an insect an insect?
One of the most defining features of an insect is not something that you’re going to immediately notice upon looking upon them, and that is, inside of the antenna, you know, the antenna has many little segments that it’s composed of. And the second one of those segments has a special name, it’s called the pedicel. And within the pedicel is this, it’s called a chordotonal organ, and it’s a highly sensitive organ that basically, to oversimplify it, picks up on very subtle vibrations.
And it can be highly attuned, so that insects can really get an amazing perception of their world through this very specialized organ. So much so that, for example, among some of the flies, it is so finely tuned and has so many nerve endings within it, they can pick up the vibration of another fly, and they’re able to tell whether that fly is of the same species, or even if that’s a male or a female of the same species.
Michael. And whether it’s a potential mate. All from the very fine vibrations it’s detecting with this very highly specialized organ in the antenna. So it really expands the sensory world of these six-legged organisms, and that is one of the most defining features of an insect, even though it’s not something you’re immediately going to look down and be like, “Wow, look at that”-
Margaret. Pedicel. [Laughter.]
Michael. … chordotonal organ.” There are also some other features. So insects have a very specialized structure at the back end of their body that the other six-legged animals do not have. It’s called an ovipositor, and it’s used, as its name suggests, to place eggs. And so it’s basically an egg-laying structure that allows insects to very precisely position eggs, most importantly, among some of the more primitive insects, in little crevices and various safe spots so that they’re not just too easily accessible by potential predators, or to desiccation, or various other factors that would reduce their fecundity.
Margaret. So we would have this special organ to feel the vibrations, and we have an ovipositor. We have six legs, so those are some of the sort of qualifications for being an insect?
Margaret. Yes. Now, I’m going to oversimplify, but insects descend from crustaceans. They came out of the sea, and onto the land, and eventually they learned to fly. Did they sort of invent flight? Is that the trajectory of their evolution, roughly? [Laughter.]
Michael. Yes. In a nutshell, yes. Insects were the first to fly. They did so about 170 million years before anything else joined them in the air. And the ones that eventually first, the next comers-along, if you will, were the pterosaurs, and they were then followed by birds, and eventually later on by bats.
But so for a vast period of time, a period of time twice that since the extinction of dinosaurs, insects were the sole thing in Earth’s skies. And they were up there, floating about, with all their aerial acrobatics, long before any vertebrate ever came along to mimic them.
And so I think that tends to get forgotten and overlooked that when one sees sort of like a bumblebee humming before a flower, or a butterfly flitting through your garden, you’re looking at the summation of more than 400 million years of evolutionary refinement, in terms of insect flight.”
what topics interest you? do tell!
I MIGHT NOT HAVE found Michael Engel’s “Innumerable Insects” book right away without a tip from a listener, and so here’s my wish for the new year: I hope you will be in touch and tell me more about what interests you–who you’d like to hear more about, or experts you’d like me to interview. Use the contact form and let me know.
And speaking of a bumblebee buzzing before a flower… In closing, I thought we could get a little dirty and sexy–like the best days in the garden–and listen to the original “King Bee” by the man who wrote it and recorded it in 1957, Slim Harpo. As Mick Jagger of the Rolling Stones said later after their own version of his blues song was released:
“What’s the point in listening to us doing ‘I’m a King Bee’ when you can hear Slim Harpo do it?”
Enjoy, and happy-merry to all of you, and see you in the new year.
the full interviews, if you missed them
- George Coombs of Mt. Cuba, on Phlox that insects love
- Doug Tallamy on nativars, and how they work (or don’t)
- Lynn Frierson Faust on fireflies
- Michael Engel on “Innumerable Insects”
- My entire archive of stories about insects and other arthropods