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Washington State University

Bug Splat Ecology

Posted by rdsayler | November 26, 2022
Dead butterflies and bees
[Photo: Dead butterflies and native bees. Photo by R. Sayler.]


Before we begin, we must deeply apologize to all of our colleagues in the Department of Entomology at Washington State University. We used the word “bug” and we knows that annoys the heck out of them. But surely they realize that we did it with entomological love in our hearts in an attempt to bring attention to the importance of their scientific field, generally thought of as the study of insects (but includes other arthropod groups like arachnids, myriapods, and crustaceans). 

See what just happened? Even trying to define entomology is complex and filled with puzzles, riddles, and millions of ecological and evolutionary mysteries yet to be discovered and solved.

As scientists in the WSU School of the Environment, we obviously know that entomology is a diverse field of scientific investigation that embodies many other specific fields of science such as molecular genetics, biochemistry, agriculture, ecology, health, paleontology, etc. 

But if a splashy or trashy “gotcha” headline works for the National Enquirer, we figure it’ll work well in entomology too. So with that mea culpa to our entomology colleagues, we begin.

If you wanted to, you could legitimately call your vehicle windshield a “splatometer” and tell people that you’re just doing scientific research when you drive around watching insects, quite unfortunately, splatting into your windshield. For many years scientists have had growing concern that insect populations are joining the numerous groups of organisms on Earth that are rapidly declining and becoming endangered or even going extinct.

You may have heard the term or phrase “Insect Apocalypse” pop up in the news in recent years. From studies in the U.K., Germany, and elsewhere in Europe, researchers began to openly explore whether long-term monitoring studies provided evidence that insect populations were declining across large landscapes. That answer essentially appeared to be “sure looks like it” which has prompted debate about having adequate long-term data to cover large regions of the Earth and reach valid conclusions about population trends.

A large-scale meta analysis of studies of insect populations reported in 2020 in Science (see: Meta-analysis reveals declines in terrestrial but increases in freshwater insect abundances.) concluded that the average decline of terrestrial insect abundance was about 9% per decade, although in some places freshwater insect abundance appeared to be increasing.

As you might expect, when it comes to the natural world, we often don’t have enough widespread and long-term monitoring data for many organisms to be 100% definitive and concrete when answering tough and complex environmental questions. 

And to make matters worse, there are untold millions of insect species on Earth, with possibly as many as 80% of insects not yet even discovered and described, let alone studied in any great detail.

But if we take a step back, in general terms, it would be surprising if many species of insects and other invertebrates weren’t being affected by the human-derived forces of climate change, habitat loss, habitat fragmentation, agriculture, light pollution at night, invasive species, and environmental degradation caused by widespread use of pesticides and other chemicals. 

Part of the debate and interest in the phenomenon of potential insect population declines has come from people, who in their lifetimes, have witnessed an apparent dramatic decline in the number of insects splatting on their windshields as they drive about. Wikipedia calls this topic the “windshield phenomenon.”

How to Use Your Splatometer

Of course, cars and other vehicles vary in their size, windshield design, and other factors, so it’s only natural that someone would standardize the measurement of insects hitting vehicles and come up with the “splatometer” – a standard card affixed over a vehicle’s license plate (that’s a registration plate in the U.K.) so that the measured surface area and general location on the vehicle are relatively constant.

Statistical modeling can then be used to account for differences in bug splats by age and models of vehicles, distance traveled, location traveled, date, etc.

Several studies using splatometers in the U.K. and Europe have suggested that insect splats have declined as much as 50-80% over times frames since the late 1990s and early in this century. But rather than repeat that information here we highly recommend that you see the following excellent article and the great information links it contains:

The Guardian: Car ‘splatometer’ tests reveal huge decline in number of insects 

How Many Insects are Killed by Vehicles?

It’s only natural to wonder how many insects might be killed by vehicles in any given area given the pervasive use of trucks and cars in developed countries. We’re not aware of large-scale and detailed estimates of insect numbers killed by vehicles except to say that somewhat ad hoc, back-of-the-envelope calculations based on the few existing studies suggests that there are trillions upon trillions upon trillions of insects killed every year by vehicles. The full ecological consequences of these losses combined with the ecology of roads and highways is relatively unknown.

What Bugs Us

You might be tempted to think: “So what? I don’t really care that much about insects. In fact, to be honest, I don’t really like bugs.” However, that would be a big mistake. As the famous biologist, E.O. Wilson once said:

“It’s the little things that run the world.” – E.O. Wilson

If you like wildlife and plants and animals in general, then what happens to insects and other critical invertebrates is central to life on Earth. Without insects, life on Earth would literally crash. As it is, declining insect populations are implicated in the decline of insectivorous birds (see: Bird declines tied to fewer insects.). 

Declining insect populations and the conservation of insects should be of concern to everyone who cares about the future of life on Earth. Perhaps the next time you’re riding in or driving a vehicle and a bug splatters on the windshield, you’ll at least cringe a little and consider the impacts that humanity is having on the untold millions of species of insects (and all other life) on Earth.


R. Sayler
WSU School of the Environment

See more at: SoE Science News 

Additional Information for the Overachievers Among Us (and you know who you are…)

Now that you’ve got a good foundation and background on the basic issues of declining insect populations from the article in The Guardian, let’s get up to speed on some newer developments using more standard techniques.

A recent study in the journal, Nature, has concluded that reductions in insects of almost 50% or more in abundance and about 27% in the number of species have occurred in some areas, particularly in the tropics where the effects of climate change and habitat loss (i.e., conversion to agriculture) are increasing (see: Climate change triggering global collapse in insect numbers, stressed farmland shows 63% decline: New Research).

“Many species are being lost before we even know them.”

And yet another new study from Brazil reported that terrestrial insects were in decline after reviewing unpublished data from 150 experts (see: Trouble in the tropics: The terrestrial insects of Brazil are in decline.).

Citizen Science

If you’re interested in how people in other countries are participating in studies of insect populations, you might enjoy the citizen science project using “splatometers” by “Bugs Matter” in the U.K.