By Margaret Carreiro, Ph.D. Biology and President of Wild Ones Louisville
As I was on my early morning “walkabout” around my “hood” earlier this week, pondering the “answer to life, the universe and everything”, I was paying attention to what people were growing in their front yards. Despite a few exceptional bursts of floral life in some yards, most yards consisted of grass and foundational evergreen shrubs, with a tree or two stuck into the lawn like lollipops. The lawn under the tree was kept immaculately shorn, and it suddenly occurred to me that I needed to write more about the importance of people creating “Soft Landings”.
Perhaps you don’t realize this, but we are in the midst of an insect extinction crisis that some scientists are calling the “Insect Apocalypse”. Insect groups that are most at risk include Butterflies and Moths (Lepidoptera) and aquatic insects like dragonflies. That’s because they have complex life cycles that depend on the quantity and quality of TWO kinds of habitats, both of which are diminishing and deteriorating across the world. Dragonflies live as nymphs in streams and ponds, while adults inhabit the terrestrial realm. Butterflies and moths at all stages of their life cycle are terrestrial, but their larval stages, caterpillars, need to eat the leaves of what we call “host plants”, before becoming pupae (called a chrysalis for butterflies; a cocoon for moths) and emerging as the beautiful adult winged creatures we “Ooh and Aah” about and love seeing nectaring on our flowers.
So, here’s the thing. To see adult butterflies, we must take care of the needs of both their CATERPILLAR AND PUPAL life stages. As people learn more about gardening with native plants, they know that it is not enough to attract adult butterflies with flowers we grow; if we have space, we know to provide the specific plants that the caterpillar stage needs to eat. Some species are picky eaters and have a narrow range of particular host plants that they will eat, while others eat a broader range of plants. However, the native plants that supply the needs of the greatest number of butterfly and moth species are TREES. Those trees that support the most species of Lepidoptera, both locally and across the country, are native OAKS, WILLOWS, and CHERRIES. But most native trees and some non-native trees support caterpillars, which by the way are the most important food source for songbirds.
THAT’S GREAT! We have learned about the importance of growing host plants, especially trees, to support CATERPILLARS. BUT WHAT HAPPENS AFTER THAT? To complete the Lepidopteran life cycle, WE NEED TO SUPPORT THE NEEDS OF THE PUPAL STAGE, TOO. This is where providing SOFT LANDINGS COMES IN.
When caterpillars on trees are getting ready to pupate, some attach themselves to the tree leaves, others crawl down the trunk of the tree to wriggle their way into the soil a bit. But, how do many home owners take care of the spaces under trees in their yards? When the trees drop their leaves (to which pupae are attached), are they saved and allowed to accumulate under the tree? Not that I’ve noticed! We blow those leaves into piles to have them bagged and carted away as if they were trash and not a valuable resource for enriching soil and sustaining soil critters. Or we mow over those leaves, thinking “what a good boy am I” for not bagging the leaves, but instead allowing the leaves to decay more quickly and add to the nutrients for feeding grass and the trees. But mowing leaves is not good for the pupa attached to them, is it?
We also kill pupae by cutting the grass under the tree to keep the yard looking “neat”. Any pupa that dropped off the tree canopy or caterpillar that crawled down the trunk then tried to wriggle its way into a compact mat of grass or compacted soil will either be ground up by a mower or become easy picking for a squirrel, chipmunk or bird, because the soil was just too hard for wriggling into.
Figure 1. A mighty oak that likely supports or could support many caterpillars of diverse moth and butterfly species. But the pupae attached to the leaves when they fall and any caterpillars that crawl down the trunk to subsequently pupate in the soil don’t stand a chance.
WHAT CAN WE DO TO PROVIDE A SAFE SPACE FOR THE PUPAL STAGE OF BUTTERFLIES AND MOTHS WHOSE CATERPILLARS EAT TREE FOLIAGE?
First of all, stop mowing under the tree canopy. Then think about what you might want to replace grass with to create a soft landing. If there’s a lot of grass to remove, you can consider weed whacking, then smothering it with wet cardboard. Next, rake fallen leaves to place atop the cardboard (to about 3 inches), wet them down, and then place branches on top of the leaves to help keep them from blowing away. Weigh the cardboard down with stones or bricks. The cardboard and leaves will decompose overwinter and by spring help make the soil beneath the tree spongier and softer and more ready to be planted in spring. Plants could include simply letting those rambunctious native violets grow into the space. Better yet, using a trowel (not a shovel) plant plugs of ferns, sedges and low-growing woodland flowering plants that are shade tolerant. You do not want to use a shovel or disturb the soil very much under a tree because you will kill the tree’s many feeder roots which are near the soil surface. These feeder roots are tiny, only a millimeter or two in diameter, and easily damaged. You also do not want to add soil or compost under an established tree because you are likely to smother those fine roots which need a fair amount of oxygen to survive. Water the small plants well for the first couple of years until you know they are rooted in and can reproduce on their own. Once the plants are established, they will continue to catch the fallen leaves from above or a bit extra that you may want to rake in there to keep the soil soft, spongy and fertilized naturally.
Figure 2. These people are at least NOT mowing under their holly tree and letting whatever plants show up grow. This is definitely better than not mowing but once the soil under the tree has had a year where leaves can decompose and soften the soil, plugs of native plants could be inserted with a trowel and make a soft landing that is more intentional.
Figure 3. A small sapling surrounded by sun-loving plants. As the tree grows it will be able to support more caterpillars and the pupae stand a better chance of surviving.
HELPING MOTHS AND BUTTERFLIES AVOID AN ECOLOGICAL TRAP
If you grow trees in grass and keep that grass mowed, what you are creating is a situation called AN ECOLOGICAL TRAP, which from a butterfly or moth’s point of view is worse than having no tree at all. Why? Because the tree entices the adult female moth or butterfly to lay her eggs on their leaves. However, because of how we manage under that tree, the situation winds up killing her children. The female might have picked another tree in a spot where her progeny would have been more apt to survive. Creating ecological traps for moths and butterflies is not what we want, I would think! Instead, we want to help them complete all stages of their life cycle and become the next generation that we can all enjoy and appreciate! Otherwise, there will be fewer butterflies and moths species that live in tree canopies with each successive generation.
Figure 4. Pupae of the Cecropia Moth (top) and the Mourning Cloak Butterfly (bottom)
Figure 5. A few of the butterflies and moths whose pupae we’d more likely save by providing soft landings below trees. Clockwise from upper right: The Rosy Maple Moth, Clymene moth, Mourning Cloak Butterfly, Coral Hairstreak Butterfly, Cecropia Moth.
If you want to know more about soft landings, see examples of how they could look, learn how to prepare the ground under a tree for planting without harming the tree, and see a recommended native plant list, I encourage you to visit: https://www.pollinatorsnativeplants.com/softlandings.html
Here is a short list of native groundcovers.
Groundcovers are low-growing plants that fill in quickly to make a dense carpet of foliage. Once established, they’ll crowd out weeds, provide year-round protection to the soil, and offer overwintering habitat for native fauna. Ideally, a groundcover should include several species combined to create a beautiful tapestry of foliage and blooms, offering a long season of interest to humans and pollinators. Choose species with a similar growth rate (aggressiveness) for low-maintenance planting. If planting around an established tree, use plugs and a trowel so as not to disturb the tree’s tiny feeder roots, not a shovel.
May-apple (Podophyllum peltatum) ● Canada windflower (Anemone canadensis) ● Eastern hay-scented fern (Dennstaedtia punctilobula) ● Big-leaf aster (Eurybia macrophylla) ● Canada wild ginger (Asarum canadense) ● Golden star (Chrysogonum virginianum) ● Wild bleeding-heart (Dicentra eximia) ● White wood-aster (Symphyotrichum divaricata) ● Creeping wood phlox (Phlox stolonifera) ● Foam-flower (Tiarella cordifolia) ● Allegheny spurge (Pachysandra procumbens) ● Golden groundsel (Packera aurea, P. rotundifolia) ● Spreading Jacob’s-ladder (Polemonium reptans) ● Solomon’s-seal (Polygonatum biflorum) ● Native violets (Viola species, blue, yellow, or white flowers) ● Glade fern (Diplazium pycnocarpon) ● Lady fern (Athyrium filix-femina) ● Sensitive fern (Onoclea sensibilities) ● Moss phlox (Phlox subulata) ● Wild strawberry (Fragaria virginiana) ● Spreading Juniper (Juniperus horizontalis) ● Golden Alexanders (Zizia aurea) ● Wild bleeding-heart (Dicentra eximia) ● Frogfruit (Phyla nodiflora)
Here is a short list of some of the butterflies and moths that use native oaks as host plants: Red Spotted Purple, Horace’s Duskywing , Banded Hairstreak, white M hairstreak, Clymene Moth, Imperial Moth, Cecropia Moth, Rosy Maple Moth, Polyphemus Moth
Here is a short list of some of the butterflies and moths that use native maples as host plants:
Rosy Maple Moth, Cecropia Moth, Oval-based Prominent Moth, Retarded Dagger Moth, Orange-humped Mapleworm, Maple looper, Baltimore Bomolocha, Imperial Moth
Here is a short list of some of the butterflies and moths that use native willows as host plants:
Mourning Cloak Butterfly, Eastern Tiger Swallowtail, Cecropia Moth, Io or Peacock Moth
Here is a short list of some of the butterflies and moths that use native cherries as host plants:
Eastern Tiger Swallowtail , Red Spotted Purple , Coral Hairstreak, Striped Hairstreak, Cecropia Moth