One of the best decisions that gardeners can make to increase the diversity of wildlife on the land that they steward is to “leave the leaves.”
This easy-to-remember turn of phrase means refraining from raking, blowing, or mowing the fall leaves that butterflies, bees, moths, spiders, toads, salamanders and other critters rely on for habitat to shelter and overwinter in. The benefits are compounded the following spring as pupating insects mature and then emerge as adults, pollinating our plants and providing food for birds and other insectivores.
Our instinct to tidy up our yards in fall is hard to defy, but our local wildlife will be better for it if we can put garden cleanup off until the following spring, after overwintering insects have come out of the leaves.
Taking it even further, you can leave the leaves permanently in unused areas of your landscape, and let it “go wild.” Plus, the leaves that you do wind up picking up — like leaves on driveways, sidewalks and paths — can be raked or blown into these areas rather than bagged and sent to a landfill.
Why Leave the Leaves?
According to the Xerces Society for Invertebrate Conservation, providing winter cover is “one of the most valuable things you can do to support pollinators and other invertebrates.”
The Xerces Society seeks to raise awareness that though some butterflies are migratory, such as monarchs, most butterflies and moths overwinter as eggs, caterpillars, chrysalises or adults in leaf litter. The same is true of queen bumblebees, which hibernate in burrows that are just an inch or two deep underground and are protected, ideally, by a thick layer of leaves.
On another front, leaf blowers cause noise pollution that can make you unpopular with your neighbors, and their fumes and the dust that they kick up is bad for air quality. Increasingly, towns are banning gas-powered leaf blowers or limiting the hours of operation. You can get ahead of this trend by setting the leaf blower aside and letting the leaves stay where they are.
Remember that leaves are bountiful in carbon and other nutrients. When we remove every leaf from beneath the tree it fell from, those nutrients are not returned to the tree.
Leaf litter is a natural mulch that, among other benefits, will prevent freezing and thawing of the soil during winter, which can damage shrubs and other plants, and the following spring the leaves will suppress weeds until you are ready to plant in the area. Leaves also improve the tilth and fertility of soil below as they are naturally broken down by mycorrhizal fungi and turned into worm castings.
The Pollinators That Overwinter in Leaves
There are countless examples of bee, butterfly and moth species that overwinter in leaves. Here are just a handful to give you an idea of the importance of leaves to all insects.
Aphrodite Fritillary – This orange-brown butterfly with interesting wing patterns has one brood per year. The females lay single eggs near violets, the Aphrodite fritillary larval host plant. The caterpillars that hatch from those eggs overwinter without eating. If the caterpillars are undisturbed and survive the winter, they eat new violet leaves in spring, doing minimal damage that the host plants can easily tolerate.
Isabella Tiger Moth – The caterpillar of this moth is a generalist feeder known as the “woolly bear” or “woolly worm.” Eggs are laid in clutches of two or three dozen, and the caterpillars hatch in the fall and then overwinter under leaves. The caterpillars will freeze solid in winter before defrosting and becoming active again in spring.
Red-Banded Hairstreak – Hairstreaks are a variety of species within the gossamer-winged butterfly family that have slug-like larva. Red-banded hairstreaks, according to the Xerces Society, lay their eggs on fallen oak leaves. Both larvae and pupae overwinter in leaves.
Luna moths – These big, beautiful green moths disguise their cocoons as dried leaves and blend in with fallen fall leaves.
Bumblebee – There are more than 250 species of bumblebee, all in the genus Bombus. Though bumblebees do not form hives like honeybees, they do have queens. Depending on species, bumblebee colonies range in population from about 50 to a few hundred, but only new queens overwinter to start the colony life cycle over in spring. The queens build sites for overwintering in rotting logs or loose dirt and depend on leaves for insulation.
Leaves, Insects and Birds
You may recall that in 2019 the journal Science published a study that showed that since 1970 the bird population in North America has declined by 29% — about 3 billion birds. While habitat loss drives much of the decline in the bird population, another major contributing factor is the collapse of the insect population.
Insects are a nutritious and vital food source for insectivorous birds and are necessary for rearing their young. Using pesticides indiscriminately or removing insect habitats such as leaf litter reduces the food that’s available to birds.
We gardeners often think of insects as either pests or beneficials, but there are far more insects that are “neutral” to us and essential to birds. Birds make meals out of insects that emerge from leaves after the winter, and they also pluck insects directly from leaf litter for themselves or for their hatchlings.
Sourcing Leaves for Compost and Mulch
Leaves provide great value to gardeners as a compost ingredient or organic mulch. If you decide to leave the leaves but still desire compost inputs or mulch, you can do what I do every November: pick up the bagged leaves that your neighbors have put out to the curb.
I collect literally hundreds of bags of leaves this way annually, because as far as I’m concerned, a gardener can never have enough leaves.
Bagged leaves are often destined for municipal composting operations, but others, sadly, will be sent to a landfill. You can do your part to reduce waste by recycling leaves on your own property — and you’ll save the insects in those bags, too.
In fall, I shred about half of the leaves that I’ve collected. The rest, I store in my leaf corral until spring, allowing the insects to survive.
Do you “leave the leaves”? Let us know by sharing in the comments below.
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Links & Resources
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