Issue 14, October 30, 2019

Leaving habitat for beneficial insects

Fall flower bed with leaf litter, Sarah Hughson, University of Illinois at Urbana-Champaign.

Holding off on some fall clean up in the home landscape can provide essential overwintering habitat for beneficial insects and beloved native species like lacewings, solitary bees and fritillary butterflies!  Here are some of the habitats these insects can benefit from:

Leaf litter

Leaf litter can be left as cover in flower beds.  It provides good shelter for overwintering beneficial insects.  Many species of bumble bees, likely including the endangered rusty patched bumble bee (Bombus affinis), overwinter in leaf litter or in the loose soil below.  Leaf litter allows insect predators, like spiders, lady beetles and ground beetles, shelter in locations close to their prey and can provide food for macro-decomposers like sowbugs.

However, if you have fruit trees with a fungal pathogen like apple scab, it is beneficial to remove that leaf litter to help reduce disease prevalence the following year.

Standing ornamental plants

Allowing some standing perennials and ornamental grasses to remain throughout the winter can provide overwintering sites for native solitary bees.  Solitary bees often overwinter inside hollow stalks, canes or other standing plant material, where they are protected from the elements.  Some species will even block the opening of a hollow stem with plant debris.

Many local fritillary species overwinter as caterpillars on or near their host plants.  Swallowtail butterflies like the eastern black swallowtail butterflies (Papilo polyxenes) overwinter as a pupa inside a chrysalis.  The chrysalises of these species are anchored to stalks or stems of plants.  Both chrysalises and caterpillars are well camouflaged, making them easy to overlook and accidentally clear away with debris.

Black swallowtail chrysalis (Papilio polyxenes), Whitney Cranshaw, Colorado State University,

Other sheltering sites

Many insects like lacewings and lady beetles, prefer to overwinter in small crevices in the landscape, including spaced between bits of bark on trees, in log piles or in small gaps between rocks.  The mourning cloak butterfly (Nymphalis antiopa) overwinters as an adult butterfly in spaces between the bark on trees, in wood piles or inside your shed.
Areas with loose soil and abandoned rodent holes can also be safe overwintering sites for some species of native bees, including some species of bumble bees.

Sarah Hughson

Return to table of contents