Leaving a layer of whole fallen leaves under trees and landscaping provides long lasting mulch and cover for overwintering insects, which become food for birds in the spring
Leaving fallen leaves as mulch benefits your plants as well as insects that need a place to overwinter. Great spangled fritillary and wooly bear caterpillars hide in the leaf litter to evade predators and to find shelter from winter weather. Luna moths and swallowtail butterflies overwinter in cocoons and as chrysalises that are colored such that they blend in with the leaves. Chopping leaves before using them as mulch increases the speed at which they break down, which is great for mulching the lawn. Shredding leaves puts these insects in danger of being shredded themselves before they have a chance to finish their life cycle as adult moths and butterflies. Insects that depend on leaf litter for shelter also require a longer lasting cover. Leaving a thin mat of whole leaves under trees allows them to break down slower and continue to provide that shelter, ensuring a new generation of pollinators and food for nestling birds in the next season.