By Pamela Sleightholm
Every autumn we’re encouraged to “leave the leaves” or to leave the garden a little messy for overwintering insects, including pollinators. A few insect species migrate over the winter and return when the weather warms again, most notable is the super-migration of monarch butterflies from here to Mexico. Others produce glycerol in their bodies that prevents them from freezing. And some will look for warm nooks in your house to get through the cold.
But other species will overwinter in your garden, and our fall yard clean up can have an impact on the species that are able to thrive over the cold period.
Autumn leaves are lovely - on the trees AND on the ground. Photo ©2021 Jeanne McRight.
Here are a few of the insects that benefit from the protection or surfaces of leaves, stems and logs.
Native solitary bees
– arguably the most industrious of the pollinating insects, native solitary bees usually build nests for their eggs to overwinter in bare soil and pithy stems.
Bumblebees
– these pollinators overwinter in underground nests and shelter under leaf litter.
Beetles
– an underappreciated pollinator group, many species burrow into bare soil until winter passes. Others, including ladybugs, are quite cold sensitive so they’ll hibernate under tree bark or in warmer areas close to the house (or in your house, if they find a way!). Fireflies, which are also a kind of beetle, will burrow underground or lay their eggs in the bark of trees or leaf litter.
Tiger swallowtail butterflies
– the chrysalis of tiger swallowtails are camouflaged to resemble leaf litter.
Mourning cloak butterflies
– they lay their eggs in brush piles and crevices within trees. Because they overwinter as adults, they’re one of the earliest species to emerge in the spring.
Luna moths
– though not a pollinator, these spectacular moths need the shelter of fallen leaves to make it through the winter.
Dragonflies
– also not pollinators and most live as nymphs under water through the winter, but some species of this very cool insect need leaf litter to overwinter.
Mourning cloak butterflies, native solitary bees and tiger swallowtail butterflies are all species that overwinter in our gardens.
What can you do?
Don’t trim back or dispose of dead stems – not only will some insects use hollow stems in your garden as their nurseries, the seed heads are a crucial food source for overwintering birds and they look stunning with a dust of snow.
Keep a small brush pile of trimmed branches or a few logs – some insects will bore into dead wood, while many other creatures will seek the protection of the brush.
Leave fallen leaves – it’s true that leaves left on turfgrass over winter can damage the grass for next season. If you still have grass, you can very gently rake the leaves into your garden beds to protect overwintering insects. In the spring the leaves will rot into your soil, adding nutrients to your beds.
Some ideas from our members on how to support overwintering creatures - clockwise from top left: a collection of pithy stems and drilled logs provide shelter opportunities; a nest within a drilled log; seed heads from Monarda fistulosa to feed the birds; a tidy brush pile tucked into an unused corner; a small brush pile hidden behind a large armour stone; bags of leaves hoarded from neighbours for extra leaf litter in the yard.
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