9 Beneficial Garden Insects That Overwinter in Fall Leaves
Autumn’s leaf drop presents a renewable resource straight from the garden. Fall leaves make an excellent mulch and soil conditioner full of nutrition, and they also create valuable habitat to foster overwintering pollinators and other beneficial insects. Explore how leaving the leaves is pollinator-friendly with gardening expert Katherine Rowe.
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Life in the garden continues in winter, even if it’s less visible. With a supportive habitat, the creatures that inhabit our gardens in spring and summer remain nearby to continue their ecosystem roles.
The fall and winter landscape is an important habitat for native bees, butterflies, and moths. These nest, lay eggs, and overwinter in fallen leaves and hollow stems. Amphibians, invertebrates, songbirds, and small mammals overwinter in the shelter of standing plants, logs, brush piles, stone walls, leaf litter, and healthy soils.
Autumn foliage has much to offer, from winter insulation for plant crowns and roots to enriching soil nutrition. There’s a world of biodiversity beneath fall leaves, which provide refuge until spring’s reemergence when beneficial insects work to balance our gardens through pollination, pest management, and increasing the food web. Leaving the leaves is a pollinator-friendly practice, just as essential as planting flowering perennials, herbs, shrubs, and trees.
How and Why to Leave the Leaves
There are several ways to make use of fall’s natural leaf drop. Let them lie in place to decompose over the season. Or, rake whole leaves into garden beds and around trees as mulch to provide insulation and soil enrichment as the leaves break down. Entire leaves are best for habitat to overwintering insects and more.
If you have excess leaves, pile them to become leaf mold. Leaf mold is a prime soil conditioner and topdressing in future seasons and winter habitat in the meantime. Wait until spring’s temperatures reach the mid-50s℉ to thin leafy layers or make use of piles.
Here are the beneficial insects that most enjoy fall leaves:
Queen Bumblebees
Bumblebee queens spend the winter beneath leaf litter, burrowing into soft soils. They’ll emerge to lead the next generation of working bees.
Queen bumblebees are the only ones to survive winter, and they hibernate alone. In spring, they surface to begin nesting, collecting pollen, and laying eggs.
Their Role
Bees are essential to flowering crops and are responsible for pollinating one-third of all plants. Some wildflowers, like monkshood, tailor their reproduction specifically to bumblebee ways – you’ve likely seen a bumblebee work its way into a tubular bloom, shaking out pollen as it shimmies to reach the nectar source. The loose pollen dusts other blooms and sticks to the bumblebee’s fuzz as it travels between blossoms.
Some bumblebees are long-tongued species, able to reach flowers with deep tubes.
How to Attract Bumblebees
Bumblebees can see ultraviolet light, and blue and purple blooms attract them. They spot yellows and other shades, too, and petal markings like speckled throats and unique shapes direct them to nectar and pollen centers.
Native wildflowers like lupine, penstemon, aster, goldenrod, columbine, and so many others are a draw. Flowering trees and shrubs, herbs, and annuals like snapdragons are other favorites.
Swallowtail Butterfly Caterpillars
Swallowtail butterflies are the beautiful yellow and black, tiger-patterned winged creatures we admire throughout the summer. In the fall, their caterpillars (larvae) attach to fallen leaves or stems and build a chrysalis. The chrysalis is a webbed cocoon that camouflages perfectly as a stick or rolled leaf.
They enter a state of diapause (dormancy) until temperatures warm. Special chemical compounds act as anti-freeze to protect them during frigid conditions. With metamorphosis, they emerge as the striking butterflies that pollinate the garden.
Their Role
The Papilionidae family has about 30 species of North American swallowtails. They visit both native and non-native plant species and travel distances to do so, increasing genetic diversity and cross-pollination. They have long tongues for reaching deep, tubular nectar sources.
How to Attract Swallowtails
Grow host plants to foster the full lifecycle of swallowtails. Hosts, depending on the species, include ash, birch, black cherry, willow, fennel, dill, rue, spicebush, sweet bay, and tulip trees. Nectar and pollen-rich bloomers like milkweed and Joe Pye weed are reliable food sources.
Fireflies
Fireflies are beetles with the special power of bioluminescence to flash in the evening sky. They are not flies but beetles, mostly active at dusk and nighttime. Some species are active during the day and use pheromones rather than flashing to communicate.
Fireflies spend much of their lives in the larval stage, from two months to two years or more. They spend this stage under leaf litter, burrowed into the ground, or in logs and decaying bark. They overwinter in these zones until emerging in spring and maturing in the summer.
Their Role
Beetles are among nature’s first pollinators. They’re important nocturnal pollinators, including Eastern fireflies (the flashing species found east of the Rocky Mountains), who feed on nectar and pollen. Fireflies are beneficial as natural pest control of soft-bodied invertebrates (slugs, snails, worms) and other insects.
How to Attract Fireflies
Aside from keeping the leaves and duff, native plants and tall grasses create habitat for fireflies. Maintaining turf around four inches high rather than clipped short is a draw. Lessen the intensity of bright outdoor lights so they can glow and communicate in darkness.
Luna Moths
Luna moths are stellar green moths that look like fresh foliage. In the larval/caterpillar stage, these beneficial insects overwinter in fall leaves and create cocoons using a leafy wrapper for insulation in winter. The leaf wrap also conceals and protects the pupae against predators until their spring emergence.
Their Role
Luna moths (Actias luna) generally add diversity and an ethereal quality to the garden. They’re not pollinators, and they don’t prey on other insects, but they do contribute to the food web. They’re a food source for songbirds, small mammals, and other insects.
Their caterpillars nibble on the leaves of nut, fruit, and flowering trees and shrubs, but they don’t pose a threat of damage due to their low population count.
How to Attract Luna Moths
Favorite hosts include American beech, birch, walnut, hickory, sweet gum, white oak, black cherry, and willows. Reduce light pollution to draw the gentle beauties.
Ladybugs
Ladybugs, the beloved spotted red beetles, nestle under leaf litter and in other protected spaces like log piles and tree cavities in cold weather. They congregate in numbers and enter dormancy until temperatures enter the mid-fifties℉ in spring. They prey on other insects that become active at the same time.
There are almost 6000 lady beetle species worldwide, with some 500 in North America. Most are predatory, and some supplement with nectar and pollen.
Their Role
Ladybugs are valuable, predatory insects that favor aphids and other soft-bodied insects. They help control populations and keep the sap-sucking pests in check. Mites, mealybugs, thrips, whiteflies, and leafhoppers are also in their diet.
How to Attract Ladybugs
Pollen and nectar-rich blooms are a way to draw ladybugs. Flat-topped flowers like yarrow, milkweed, alyssum, calendula, and dill are good food sources. The presence of aphids, too, will keep them visiting.
Leafcutter Bees
Like the American bumblebee, leafcutters are native bees. They’re solitary, meaning they don’t colonize or have a queen to defend, and are nonaggressive as a result (and have a milder sting if handled). They cut little half-moons out of leaves to make nests, though the cuts are minor for the plant.
Solitary bees overwinter in the pupal stage. The adult female leafcutter places singular eggs in a nested cell of pollen and nectar and seals it with leaf cuttings for insulation and disguise. When it hatches, the larva feeds on the pollen and nectar and spins a cocoon to pupate until temperatures warm. Leafcutters are one of the last to emerge in spring.
Solitary bees seek out a variety of sites to nest, from soft, dry spots underground to rotting wood/logs, between stones, hollow stems, or other small openings (pencil-size). Autumn leaves help protect solitary bees who nest on the ground level. Mining bees (Andrena spp.), cellophane bees (Colletes spp.), and sweat bees (Agapostemon spp.) dig ground nests.
Their Role
Leafcutter bees pollinate many flowering selections, from ornamentals and wildflowers to crops like blueberries, carrots, tomatoes, peppers, squash, and others. They’re efficient pollinators and farmer favorites for moving more quickly than honeybees as they carry pollen between blossoms.
How to Attract Leafcutter Bees
Leafcutters need blooms for pollen and nectar and fresh leaves and petals for nesting. Flat, open-faced flowers like asters, sunflowers, rudbeckia, heliopsis, and echinacea provide easy pollen access. Leaves from roses, ash, lilacs, azaleas, hostas, and peas are favorite sources.
Fritillaries
Fritillary butterflies, also called silverspots, resemble monarchs in their coloration and size but with checkered wing patterns. Metallic spots on the underside of their wings give a dappled camouflage effect.
There are greater and lesser fritillary species. The great spangled (Speyeria cybele) is a recognizable fritillary due to its size and wide range in the northern U.S. and southern Canada.
Fritillary females lay eggs in late summer near violets and their roots or in shady spots on the ground where violets are likely to grow. When the caterpillars hatch in the fall, they tuck themselves into leaves and enter diapause until spring. They emerge at the same time the violets show new growth. Gulf fritillaries (Agraulis vanillae) in the southern U.S. to Mexico, Central, and South America use passionflower as larval hosts.
Their Role
Fritillaries flutter through the garden, pollinating a variety of blossoms as they visit for pollen and nectar.
How to Attract Fritillaries
Fritillaries favor long, tubular blooms but also visit those with open, accessible centers. Anise hyssop, milkweed, Joe Pye weed, and lilac are attractive options. The larvae feed on violets, so these are essential to foster the population. Gulf fritillaries rely on passionflower (Passiflora spp.).
Red-Banded Hairstreaks
The red-banded hairstreak (Calycopis cecrops) is an attractive butterfly with tawny wings and a distinctive orange-red stripe. Their range is much of the southern U.S., from Maryland west to Kansas and south to Texas and Florida. However, their range may be expanding – New York sees them, too. The chrysalids and caterpillars (both beneficial insects) hibernate in fallen leaves for insulation. Oaks are a favorite.
Their Role
Like all butterflies, red-banded hairstreaks serve as valuable pollinators.
How to Attract Red-banded Hairstreaks
Bayberries, wax myrtles, sumacs (Rhus species), and oaks draw these butterflies. Yarrow, coreopsis, sunflowers, milkweed, and wild cherries provide beneficial food sources.
Woolly Bear Caterpillars
Woolly bears are the cutest-sounding fuzzy insects around. These caterpillars become the Isabella tiger moth (Pyrrharctia isabella), nondestructive harmless moths that don’t feed in adulthood. Woolly bears occur in the U.S., Mexico, and southern Canada.
Woolly bears have a protective hairy coat that insulates them in cold conditions. The coverage is dark at both ends, with a rust-colored central segment. Lore has it that in mild winters, their wool coats are more brown, with thicker, broader, dark segments if a colder season is in store.
Woolly worms nestle into litter and rock crevices for dormancy. They freeze until spring’s warmth.
Their Role
Isabella tiger moths aren’t pollinators since they don’t feed. The caterpillars eat leafy, herbaceous plants but won’t impact health. The benign creatures are a valuable food source for birds, small mammals, reptiles, and amphibians.
How to Attract Woolly Bears
Woolly bears eat cultivated and wild, weedy selections like dandelion and clover. Aster, goldenrod, birches, and maples are productive leaf sources.
