Marlene Condon: Keeping leaves where they fall can save butterflies, moths and other critters (2024)

Fall is the time in which we’re treated to a colorful show of leaves, courtesy of our deciduous trees. As chlorophyll breaks down and reveals a variety of hues (the result of sugars that were in the leaves all along, but masked by the green chlorophyll), these trees give us a spectacular display of natural art (as long as soil moisture and temperatures have been conducive to this outcome).

Yet, to most people, the minute those lovely leaves fall to the ground, they become litter to be bagged and hauled off the property, or worse yet, burned. These actions are disastrous for our wildlife and not at all helpful to the trees either.

Leaves are supposed to remain around the tree from which they came because they are, literally, nutrients that have been taken from the soil and transformed into leaves. After the leaves fall to the ground, they are supposed to be recycled back into the soil to nourish the tree’s future growth.

Nutrient recycling is accomplished by numerous kinds of critters that feed upon the leaves and break them down. The nutrients from the leaves are returned to the soil in the droppings of these animals. In other words, the leaves, along with the help of wildlife, constitute your natural — and absolutely free — fertilizer program.

Additionally, those leaves are your natural mulch that maintains soil moisture and moderates soil temperatures for the benefit of the tree’s roots. It’s wasteful of time, money and effort to get rid of leaves only to replace them with some other kind of mulch from the store.

But most importantly of all, those fallen leaves become an incredibly important blanket for the benefit of numerous invertebrates out there (and even some vertebrates, such as our tree frogs) that require this covering to get through the winter.

For example, female fritillary butterflies (we have several species in our area) lay their eggs in late summer near violets, the gorgeous host plants for their caterpillars that will hatch out shortly. But those tiny caterpillars will not feed this fall. They will take shelter in leaves and other plant debris to hibernate. When the violets resume growth in the spring, the caterpillars will start feeding and resume their own growth as well.

Thus if you want to create a habitat for these attractive butterflies, it’s essential to provide leaf mulch as well as violets. And these aren’t the only butterfly species that absolutely depend upon leaves to perpetuate their kind.

The red-banded hairstreak, a small but attractive butterfly, does not lay its eggs upon its host plant, winged sumac. Instead, the female attaches each tiny egg to the bottom side of a fallen leaf below the plant from which the leaf dropped. When the eggs hatch, the caterpillars feed upon the decaying leaves instead of fresh ones as most other caterpillars do. And if the caterpillar is from a late-summer brood, it will overwinter among that same leaf mulch.

The caterpillars of tawny emperors and hackberry emperors curl dried brown hackberry leaves around themselves to overwinter. Some lepidopterists (scientists who study moths and butterflies) say they remain attached to the tree, but others report that they fall to the ground when the leaves fall off their host trees. If you run a lawn mower over the fallen leaves, or bag or burn them, you kill your caterpillars and thus your future butterflies.

And, of course, our moths — being closely related to butterflies — also require leaf mulch for some species. The familiar woolly bear caterpillar, the larva of the Isabella tiger moth, was formerly spotted along roadways in September because it was searching for an area of sufficient leaf cover under which to hibernate. When spring arrived, it would pupate (form a cocoon) and finally emerge in its adult stage. Sadly, these caterpillars have greatly declined; I never saw a one this year.

Have you ever seen the gorgeous, pale-green luna moth? With a wingspan up to4 1/2 inches, it’s one of our largest moths and was the animated insect in TV commercials for the sleep aid named Lunesta.

This beloved species even appeared on a first-class postage stamp (22 cents) back in 1987.

The caterpillar can feed upon the leaves of a variety of trees and shrubs, such as black walnut, persimmon, hickories, sweet gum and sumacs. It has also been found less frequently upon red maple and white oak.

When it’s fully grown at about 2 1/2 inches, the caterpillar wraps itself in a leaf, entering the pupa stage. If this occurs as winter is approaching, the cocoon falls to the ground as the tree loses its leaves, where it’s sheltered in the leaf mulch.

Of course, butterflies and moths represent just a fraction of the many invertebrates that make use of leaf mulch. But as you can see from just the few species of butterflies and moths that I’ve written about here, keeping leaves under the trees from which they came is literally a matter of life and death for many species of wildlife.

Years ago, the luna moth was common, but it is now feared that they are endangered in some areas due to habitat loss and other factors, such as lights left burning all night. Usually when we hear that term, habitat loss, we only think about plants disappearing. But in the case of the luna moth, the problem is not a loss of trees and shrubs, but rather the loss of leaves as people insist upon removing them from their yards.

Here are some tips on how you can be more nature friendly while simultaneously lessening your load of work in the fall:

Don’t plant grass underneath trees. It doesn’t belong there; leaf mulch does.

It’s best not to plant anything underneath trees, because you shouldn’t be walking there a lot to tend to plants. Your weight compacts the soil, which is harmful to the tree’s roots. But if you feel driven to decorate the area, plant only shrubs that are meant to grow among fallen leaves and place them near the drip line.

If the autumn weather is drier than usual and the leaves are being blown out from under the tree, retrieve some pruned tree and shrub branches from your brush pile (every yard should have at least one) and place them gently over the leaf area beneath the tree. They will help to keep the leaves in place.

When I see bags and bags of leaves lining roadways to be picked up, I see mankind’s ignorance about the everyday impact humans have upon the natural world, which is accompanied by an appalling lack of concern about living in agreement with nature. I also see a world that has become — and every day is increasingly becoming — not only far less enchanting, but also far less capable of supporting us.

Marlene A. Condon, author-photographer of “The Nature-friendly Garden” earned a degree in physics and has written about nature for more than 30 years. Her articles are always based upon personal observations and documentation of the natural world. She writes a blog at indefenseofnature.blogspot.com.