As the magic of fall time fades into piles of leaf litter, many of us become focused on cleaning up the landscape before snow flies. Few of us are thinking of warm summer days filled with blooming plants and pollinating insects.
However, our actions right now during fall cleanup can have lasting impacts on the wildlife in our communities. As we neatly clean our landscape for winter, we are unknowingly removing highly valuable habitat for overwintering insects, and these tiny members of our global ecosystem are in some serious need of our help.
In recent years, the scientific community has observed drastically declining insect populations around the globe, making reference to an ongoing “Insect Apocalypse.” However, past public attention has been focused on larger, more charismatic organisms, such as penguins and pandas.
Conversely, the majority of biomass across global ecosystems resides in smaller animal life, such as insects, and they have proved to have far greater importance on the global scale than their larger and more recognizable cousins.
Insects and other invertebrates comprise the base of food webs, making their presence vitally important for all biota. If we keep losing the basic building blocks of the food web, we risk cascading effects further up the system that will affect all organisms, including humans.
Until recently, few long-term data sets were available to assess insect decline. However, two long-term studies from Germany and Puerto Rico really paint the picture with recently published results showing a
75 to 95 percent decline in insect biomass over a three-decade period of study.
North American insect populations have shown similar drastic declines that are also startlingly apparent when long-term data are assessed. A study published in 2009 by researchers at the University of Illinois compared a century of data on bumblebee populations in Illinois to uncover major declines much closer to home.
Comparing baseline data from Illinois Natural History Survey insect collections and to field-collected samples in 2007, researchers were able to assess the long-term trend for some bumblebee populations in Illinois. The study found that half the bumblebee species included in the study and historically found in Illinois were either absent or suffered major declines.
Habitat reduction and land-use change were cited as the major contributors of bumblebee decline in Illinois. As agriculture has intensified across Illinois over the past century, we have simply removed many of the habitat features these animals need from the landscape.
But what does habitat for bumblebees and other native bees really look like? Most of us think of flowers and pollination and often relate nicely arranged landscapes of native plants as the most important habitat. While nectar and pollen from native plants are vitally important food sources, bees have other habitat needs as well.
Bumblebees are unique in that their queens live the longest of any native bee, with a life span of about 12 months. Consequently, they must seek out a suitable overwintering location to hibernate until spring. They do this in the soil and leaf litter, by seeking out locations that are well insulated and not subject to wide temperature swings.
Leaves are an important insulation source for the soil. By removing all leaves from the landscape, we create a less-protected soil surface, offering less insulation for sensitive overwintering bumblebee queens.
These queens are the only members of bumblebee colony to overwinter; all others die as cold weather sets in. If this queen does not make it until next year, there will be no colony.
Beyond bumblebees, many other pollinators use leaf litter for overwintering. A number of moths and butterflies overwinter in a chrysalis buried in leaves. In fact, some chrysalises mimic the appearance of leaves, making them almost indistinguishable. So, leaf removal or burning can directly extirpate these species from your yard.
As you work on fall cleanup, keep overwintering insects in mind and look for places to maintain leaf cover. Landscaping beds, borders and fence lines are great out-of-the-way places to leave some leaves for wildlife and perpetuate their populations here.
Ryan Pankau is a horticulture educator with the UI Extension, serving Champaign, Ford, Iroquois and Vermilion counties. This column also appears on his ‘Garden Scoop’ blog at go.illinois.edu/GardenScoopBlog.