Leave the Leaves!
Most moths and butterflies overwinter in the landscape as an egg, caterpillar, chrysalis, or adult. Examples include Great spangled fritillary, wooly bear caterpillars, red-banded hairstreaks, luna moths, swallowtail butterflies, hummingbird moths, Baltimore Checkerspots and Mourning Cloaks. Leaving the leaves means you are leaving the protective leaf layer they need for survival.
This means don’t shred leaves either. You can easily destroy a butterfly egg, a caterpillar or a chrysalis of something wonderful such as the Clearwing Hummingbird Moth!
A thick layer of unshredded leaves also helps insulate mated queen bumblebees who winter just an inch or two below the soil surface.
A good leaf layer is as good as (actually better) than wood mulch. It suppresses weeds, holds soil moisture and protects tender perennial roots from frost heave. And you don’t have to remove them in the spring. Decaying leaves replenish soil organic content and help maintain soil health.
Many other invertebrates that serve as food for birds, herps, and small mammals also take winter shelter in leaf litter, old logs or brush piles.
Leave the stems too! Illinois has over 500 species of native bees. About 30% nest in holes such as those found in hollow stems and dead wood and will re-use them in the spring. Carpenter bees actually excavate holes in wood to lay their eggs.
There are many many reasons to learn to work with nature rather than against it!
A Litter Example:
Who would believe this lovely luna moth comes from this cocoon where it will overwinter in leaf litter? Could you have raked this up into your curb leaf pile?