The Windshield Phenomenon: Quantifying the Rapid Global Decline of Biomass

If you took a road trip a few decades ago, you likely remember having to frequently clean bug splatters off your car. Today, a long drive usually results in a surprisingly clean windshield. This anecdotal observation is known as the windshield phenomenon. It is backed by decades of compiled entomological data pointing to a catastrophic drop in global insect populations.

The Data Behind the Disappearance

For years, scientists noticed fewer insects in their local environments, but they lacked the long-term data to prove a global trend. That changed significantly in 2017.

The Krefeld Study

The most shocking data came from the Krefeld Entomological Society in Germany. A dedicated group of entomologists had been setting up Malaise traps (tent-like structures that catch flying insects) in 63 protected nature reserves across Germany since 1989. When researchers analyzed the collected biomass in 2017, the results were staggering. They recorded a 76 percent decline in flying insect biomass over a 27-year period. During mid-summer peaks, the decline reached as high as 82 percent. Because these traps were located in protected nature reserves, the findings proved that insect loss was not limited to heavily industrialized or agricultural zones.

Puerto Rico’s Vanishing Arthropods

In 2018, biologist Bradford Lister returned to the Luquillo rainforest in Puerto Rico, a site he had extensively studied in the 1970s. He and researcher Andres Garcia found that the biomass of ground-dwelling insects had fallen by 10 to 60 times since his original research. Sticky traps used to catch insects in the forest canopy caught up to 30 times less biomass than they did four decades earlier.

A Global Perspective

To understand the global scope of the issue, researcher Roel van Klink and a team of scientists published a massive meta-analysis in the journal Science in 2020. They compiled data from 166 long-term surveys across 1,676 global sites. The analysis revealed that terrestrial insects are declining at a rate of roughly 9 percent per decade. While the study did note an 11 percent per decade increase in freshwater insects due to clean water initiatives, terrestrial insects make up the vast majority of global insect biomass.

Primary Drivers of Insect Decline

The rapid disappearance of insects is not caused by a single event. It is the result of multiple compounding pressures created by human activity.

Habitat Loss: The conversion of natural environments into agricultural fields and urban sprawl removes the specific plants insects need to feed and reproduce. The Monarch butterfly population in North America has plummeted by over 80 percent since the mid-1990s, largely due to the eradication of milkweed plants along their migration routes.
Pesticide Use: Modern agriculture relies heavily on chemical pest control. Neonicotinoids, a class of neuro-active insecticides like imidacloprid, are highly toxic to bees and other pollinators. Even at sublethal doses, these chemicals impair navigation, reproduction, and foraging abilities in beneficial insects.
Climate Change: Insects are highly sensitive to temperature fluctuations. Extreme heat, extended droughts, and unseasonal frosts disrupt their life cycles. In the Luquillo rainforest study, researchers attributed the massive biomass drop directly to a 2.0 degree Celsius rise in average maximum temperatures since the 1970s.
Light Pollution: Artificial lights disrupt the navigational abilities of nocturnal insects. Moths and beetles become trapped circling streetlights until they die of exhaustion or are eaten by predators, preventing them from mating or pollinating night-blooming plants.

The Ripple Effects on Global Ecosystems

Insects are the structural foundation of the global food web. When their biomass drops, the effects ripple upward through every trophic level.

The decline of insect populations is directly linked to the steep drop in global bird populations. In 2019, a study by the Cornell Lab of Ornithology reported that North America has lost nearly 3 billion birds since 1970. The sharpest declines were seen in aerial insectivores (birds that eat flying insects on the wing) such as swallows, swifts, and nightjars. Without insects to feed their young, these bird species simply cannot sustain their population numbers.

Human food systems are equally vulnerable. Approximately 75 percent of all global crop types rely on animal pollination to some extent. Without wild bees, hoverflies, and beetles, the agricultural yields for crops like almonds, apples, blueberries, and cacao would plummet. Replacing the natural pollination services provided by insects with manual human labor or drone technology would cost the global agricultural industry billions of dollars annually.

How Scientists are Tracking Biomass Today

To prevent further loss, researchers are modernizing how they monitor insect populations. Traditional Malaise traps are now supplemented with advanced acoustic monitoring devices that record the hum of insect wings to identify specific species and estimate local densities. Entomologists are also using weather radar networks, originally designed to track rain, to monitor massive swarms of migrating insects high in the atmosphere. These high-tech methods provide real-time data, allowing conservationists to identify exactly where interventions are needed most.

Frequently Asked Questions

What exactly is biomass? Biomass refers to the total mass of living organisms in a given area. In entomology, researchers often measure insect biomass by weighing all the insects caught in a trap over a specific period, rather than counting individual bugs.

Are all insect populations declining? No. While the overall global trend for terrestrial insects is deeply negative, certain groups are thriving. Freshwater insects (like dragonflies and mayflies) have seen population increases in areas where environmental regulations have successfully cleaned up polluted rivers and lakes.

What can an individual do to help insect populations? You can support local insect populations by planting native flowering plants, reducing or eliminating the use of cosmetic pesticides in your yard, and leaving leaf litter on the ground during the winter. Leaf litter provides essential overwintering habitat for caterpillars, bumblebee queens, and fireflies. Turning off unnecessary outdoor lighting at night also helps nocturnal insects survive.