Insect populations plummeting, and we should worry

There’s an old joke about what goes through a fly’s mind as it hits your windshield.

Problem is, not many insects hit windshields anymore, and we might be the butt of that joke.

Biologists have slowly realized our windshields are cleaner these days, even after long highway trips. (I first drove to Death Valley from Indiana to study ant colonies in 1974. I stopped as often for visibility as I did for fuel.)

But the “windshield phenomenon,” as it is known, suggests something much larger and potentially ominous is underway at the interface of modern humanity and insects. Simply put, there are fewer insects.

Insects are the most ubiquitous group of organisms in the world. They are the largest group of arthropods, and arthropods are 80 percent of all described animal species. Insects play dominant roles in most landbased ecosystems. They pollinate most agricultural crops, cycle nutrients and provide structural complexity and stability to natural food webs.

For some time, studies of single species have suggested that populations of iconic species such as monarch butterflies are crashing. Annual surveys of monarchs wintering in Mexico reveal population declines exceeding 80 percent over the past two decades.

Rusty patched bumblebees once thrived throughout the Midwest, including Ohio. The U.S. Fish & Wildlife Service reports that they have declined 87 percent over the past two decades. They likely live in one-tenth of 1 percent of their former range.

Detecting possible steep declines in insect populations requires long-term, broad-scale studies. Those require funding and professional expertise.

Fortunately, several long-term surveys exist. Publications based on them support what biologists are seeing through their windshields. A New York Times magazine cover story two months ago declared it the “Insect Apocalypse.”

A 2017 paper in the journal PLOS One reports total insect biomass in German nature reserves declined 76 percent in 27 years. A 2018 paper in the Proceedings of the National Academy of Sciences reports a 63-fold (not percent) reduction in insects captured on sticky traps on the floor of the U.S. El Yunque National Forest in Puerto Rico over the past 40 years. The authors also observed decreases in forest insect-eating birds, frogs and lizards.

Global climate change might account for the demise of insects in tropical areas such as Puerto Rico. The apparent drivers in temperate areas such as Germany are likely more complex. Those drivers include ongoing intensification of agricultural practices and pesticide use.

Making the apparent insect collapse even worse, a recent American Entomologist paper documents the disappearance of insects from college introductory biology textbooks. The authors found that a century ago, textbooks devoted 8.8 percent of their pages to insects and their interactions with humans. Textbooks published since 2000 devote less than 0.6 percent of their pages to insects, with even less emphasis on human-insect interactions.

Topics such as modern molecular genetics, exciting to instructors who adopt textbooks, crowd out topics possibly more relevant to students, especially in general education courses.

As humanity disrupts and reduces our planet’s natural systems, responsible citizens and the policymakers they elect eventually will need to develop policies that mitigate and respond to changes such as massive losses of insects.

This is no time to drive blindly into that future, even if our windshields are eerily clean.

Steve Rissing is a biology professor at Ohio State University. steverissing@hotmail.com