Other Reasons We Should Worry About the Decline in Bug Populations
By Leslie A. Cameron, Extension Master Gardener
Insects provide critical services to our ecosystems. They pollinate our food crops and many other plants; birds and many other animals rely on them for food and to raise young; they play a critical role in decomposition and returning nutrients to the soil; and they keep populations of pest insects down.
Recent studies are documenting dramatic declines in the number and diversity of insects around the world. Entomologists, ecologists, and other scientists are expressing shock at the speed and scope of these losses, and they are pointing to these steep declines as a sign of broader ecosystem collapse.
Staggering Declines in Insect Populations
In 2017, an entomological society in Krefeld, Germany published the results of nearly three decades of careful monitoring of flying insects in 63 natural reserves in Germany. They found that the total weight (biomass) of insects had decreased by a staggering 75% over those 27 years.
In a 2019 article in Biological Conservation, Sánchez-Bayo and Wyckhuys reviewed more than 70 reports of insect decline from around the world and found evidence of similar declines of many species in many locations. From a few of these 70-plus studies:
- In a rain forest in Puerto Rico, Lister and Garcia found that over just 36 years, the biomass of arthropods in sweep samples had decreased 4 to 8 times, and biomass in sticky traps had decreased 30 to 60 times (not percent, but up to 60-fold). They also found sharp declines in lizards, frogs, and birds, which rely on arthropods for food. They concluded that these declines were “indirectly precipitating a bottom-up trophic cascade and consequent collapse of the forest food web.”
- A study in Belgium reported that 19 of 64 species of butterfly (Lepidoptera) had gone extinct since 1834, and 69% of remaining species were steadily declining.
- The Illinois Natural History Survey showed that half of 16 bumblebee species (Hymenoptera) had declined from 1900 to 2007, and 4 species had become extinct. Other researchers found declines in 52% of wild bee species in Britain and 67% in the Netherlands after 1980. In the United States, honeybee populations that peaked at 6 million in 1947 have declined by 3.5 million over the past 60 years.
- A study in the Netherlands, Belgium, Luxembourg, and Denmark found that 34% of over 400 species of ground beetle (Coleoptera) declined between 1950 and 1980.
Sánchez-Bayo and Wyckhuys estimated that roughly 41% of insect species are in decline, twice as high as for vertebrates. They estimated that around a third of all species are threatened with extinction in the countries included in the studies. They believe we are in the midst of the largest extinction event on Earth since the late Permian (248 million years ago) and Cretaceous periods (over 65 million years ago).
Contributors to the Decline in Insects
Researchers are attributing the declines to habitat change, pollution, biological factors, and climate change. Habitat change resulting from development for housing and transportation, urbanization, intensive agriculture, and other land use changes have shrunk and fragmented natural habitats. Major insect declines coincided with the shift in agricultural practices in the 20th century toward industrial scale production, monocultures, and the widespread use of synthetic fertilizers and pesticides, the removal of hedgerows and trees, and changes in land surface for irrigation. In South America, Africa, and Asia, deforestation is the main contributor to the decline in diversity and number of insects.
Pollution resulting from the synthetic fertilizers and pesticides used in agriculture, leaching of sewage, and industrial chemicals is a major contributor to insect decline. Agricultural practices associated with intensive crop production often include the widespread use of insecticides, herbicides, and fungicides. Insecticides are by far the most toxic to all insects and other arthropods, followed by fungicides. While herbicides are not as toxic directly, they reduce the diversity of plants in and around fields.
Impact on Our Ecosystem
“You have total ecosystem collapse if you lose your insects. How much worse can it get than that?”… If they disappeared, “the world would start to rot,” according to University of Delaware entomologist Doug Tallamy (Borenstein, 2018, p. 2).
Insects are critical to life on our planet. They pollinate 75% of the crops humans depend on, which make up around a third of the food supply from farms, and more than three quarters of wildflowers. Many birds, fish, and other animals rely on insects for food or need them to rear young. Insects play an essential role in the decomposition of plants and animals, returning nutrients to the soil. They also provide natural pest control and keep down the populations of many pest insects.
North America has a billion fewer birds than it did 40 years ago, according to Partners in Flight (PIF), a network of more than 150 organizations working to halt and reverse the decline in bird populations. PIF identified 86 of 450 breeding species as vulnerable and predicted that some populations would be cut by half within decades. The two groups of birds most affected are grassland birds, whose habitat has been converted to farmland, and insect eaters. Other animals are declining in number and diversity as well.
What We Can Do
“We can no longer landscape with aesthetics as our only goal. We must also consider the function of our landscapes if we hope to avoid a mass extinction that we ourselves are not likely to survive,” says University of Delaware entomologist Doug Tallamy (Tallamy, 2009, para. 20).
We can re-create biodiversity in our yards, gardens, patios, and balconies, rebuild wildlife habitats, and reduce our carbon footprint:
- Eliminate or minimize the use of synthetic fertilizers, insecticides, herbicides, and fungicides.
- Avoid nonnative plants, shrubs, and trees, especially invasive species, and plant native plants.
- Leave the spent flowers and stalks standing in our gardens and yards over the winter, let the grass grow a little longer, and let the wildflower “weeds” bloom.
- Provide a water source in our gardens and yards for insects, birds, and other wildlife.
- Do what we can to mitigate our impact on the environment where we are—buy food from local suppliers; buy organic food and grow our own; reduce, reuse, and recycle.
Sustainable landscaping and gardening, native plants, protecting insect populations, protecting yourself from mosquitoes and ticks without harming pollinators, and more.
- Virginia Cooperative Extension Arlington/Alexandria Office
- Arlington Regional Master Naturalists
- The Capital Naturalist Blog
- Plant NOVA Natives
- Partners in Flight
- Borenstein, S. (2018, September 20). Bye bye bugs? Scientists fear non-pest insects are declining. AP News. Available from https://www.apnews.com/eccd411638994db6b5388c052c00dd3b
- Lister, B.C., & Garcia, A. (2018). Climate-driven declines in arthropod abundance restructure a rainforest food web. Proceedings of the National Academy of Sciences, 115(4), E10397-E10406. Available from https://www.pnas.org/content/115/44/E10397
- Sánchez-Bayo, F., & Wyckhuys, K.A.G. (2019). Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation, 232, 8-27. Available from https://www.sciencedirect.com/science/article/abs/pii/S0006320718313636p-content/uploads/2019/02/2019_Sanchez-Bayo-Collapse-of-insect-fauna.pdf
- Tallamy, D. (2009, Autumn). A call for backyard diversity. American Forests Magazine. Available from https://www.americanforests.org/magazine/article/backyard-biodiversity/