Butterflies disappear in Ohio. This is what it means for insects from all over the world

For my eleventh birthday, I received a fun strange and weird entertainment: a book filled with pictures and descriptions to help children decode the splatters of insects that ended up in the water. before a moving vehicle. Whether it sounds gruesome to you or complains about keeping the windshield clean, a sharp drop in bugs reported in recent years should actually worry us, say entomologists and environmentalists.

In a new study published Tuesday in PLOS ONE, a group of researchers analyzed one of the few data sets to track butterfly abundance, based on 21 years of volunteer surveys in Ohio. They found an average population decline of 2% per year, which means that during the study, Ohio lost more than a third of its butterfly population.

Some butterfly species, however, have not changed in abundance and some others have become more common.

"Everything will not decline in exactly the same way," said Corrie Moreau, entomologist and evolution biologist at Cornell University, who did not participate in the new research. "But we see, in this study and others, that insects are falling fast."

Many motorists tell stories about strangely clean windshields, and bikers have noticed that they are much less likely to swallow these insects during their journeys. Articles denouncing an upcoming "apocalypse of insects" have been published on information platforms such as the New York Times Magazine and National Geographic. The Guardian claimed that the estimated rate of decline meant that insects, as a whole, could disappear within a century.

The Atlantic, by contrast, interviewed skeptical researchers about this assertion. After all, while some insects are affected by habitat loss, pesticide use and climate change, others benefit from urban environments and human intervention.

Why is there no consensus on what is going on and how bad is the decline? "We had an abundance of anecdotes, but little data was collected very rigorously," said Arthur Shapiro, an evolutionary ecologist and biogeographer from the University of California, Davis, which has been monitoring butterfly populations in California for half a century. "This means that every data set is extremely welcome and extremely valuable," said Shapiro, who did not participate in the new study.

The decline of the Ohio butterflies is a harbinger of problems for insects in general – bees, beetles, dragonflies, etc. An overall reduction in the number of insects and the eventual loss of certain species of insects would have a serious and significant effect, said Moreau. Problems for butterflies could indicate problems for bees, flies and other insects that together are responsible for the pollination and growth of up to three quarters of all crops for human consumption. In the meantime, we would lose a great diversity of insectivorous birds, bats and amphibians, with cascading effects on almost every ecosystem on the planet.

What scientists did

In the state of Ohio, thousands of volunteer scientists are walking trails known for over 20 years with a specific task. By browsing the chosen trail each week from April to October, they identify and count all the butterflies that they can see at a certain distance from their path. Later, they submit this information to The Lepidopterists of Ohio, a non-profit organization dedicated to the conservation and appreciation of butterflies, captains and moths.

When environmentalist Tyson Wepprich of the University of Oregon chose his postgraduate projects in 2017, use Ohio's data to measure long-term changes in the number of butterflies "Did not seem to be an exciting science," he said.

But as public interest in the decline of insects increased, Wepprich realized that he had an opportunity in the project led by volunteers in Ohio.

Wepprich and his team used more than 24,000 volunteer butterfly surveys to chart butterfly populations in Ohio every year between 1996 and 2016. It's not as simple as simply adding all the surveys of a given day, though – one of the challenges of participatory science is that the observations can vary considerably, observers learning to identify more species, to be replaced by other volunteers or to miss weeks of data collection.

UC Davis biologist Shapiro has been conducting his own surveillance of butterflies in California for more than 40 years. His work, which visits 10 sites on the shores, valleys and mountains of central California, is one of the few long-term projects on insect abundance in North America.

"In many ways, it's a better-designed study than mine, because mine has never been designed to be a long-term surveillance study," Shapiro said. Although its data was designed to track short-term variations, the Ohio study was "designed from the ground up" to take advantage of a dedicated volunteer force willing to collect information annually in the near future .

What they found

The total number of butterflies in Ohio has decreased from year to year over the past two decades – about 2% per year. When researchers compared this rate with other long-term studies, the overall decline is consistent with the results of surveillance programs conducted in the United Kingdom, the Netherlands and Spain.

However, the team wanted to understand why some butterfly species were more affected than others and why some of them had increased their populations during the study.

They searched to see if the related butterfly species were all better or worse and did not find any motive.

On the other hand, they noticed that butterflies more common in southern Ohio tend to do better than more northern butterflies, perhaps because they are already better adapted to react to the global warming of the planet.

"There are also some strange cases," said Wepprich. "Indigo wild indigo," a brown butterfly with mottled wings about one and a half inches in diameter, "" is doing very well in Ohio, because a plant it eats is used to fight erosion on construction sites. That's three times more than 20 years ago. "

It's intriguing, he said, because it demonstrates the massive – and fast – effect that humans can have on insects with the dedication of relatively minor resources. This is a note of optimism in a general trend of bad news.

Why is it important

Butterflies pollinate flowers, control plant populations by nibbling leaves on leaves and provide food for other insects, birds, amphibians and mammals. Their decline could have cascading effects on forests, grasslands and even the backyards of North America – vital wild habitats for an abundance of living creatures.

But butterflies also act as big and brilliant warning signs for environmental changes. "I think for most of us, entomologists, the data on butterflies are considered a proverbial canary in the coal mine," said Shapiro.

The decline of butterflies in Ohio has been captured by statistics and recorded data rather than anecdotes, but the scientific literature is also full of anecdotes. A recent article by experienced researchers, Daniel Janzen and Winnie Hallwachs, a couple who have been studying tropical ecology in Mexico and Central America for half a century, warns that insects around the world are experiencing "declining progressive and very visible ".

The solution to the worldwide decline of insects will not be simple. "If it was only one thing, we would know how to solve it," Moreau said. "But I think of the situation as, like, death by a thousand cuts."

Habitat loss, the use of pesticides over vast areas of cropland, and climate change all contribute to the disruption of natural systems. Researchers believe that any solution to a general decline in insects will need to take into account these three factors.

But complexity and uncertainty are not an excuse to sit idly by, Moreau, Shapiro and Wepprich agreed.

"I think we know enough to act now," said Wepprich.