MANHATTAN, Kansas — Ellen Welti has a Ph.D. in, essentially, grasshoppers.
And yet she was still mystified about why the number of grasshoppers in a long-protected and much-studied patch of Kansas prairie was dropping. Steadily. For 25 years.
After all, the grass that the springy bugs feast on had actually grown more robustly as it absorbed mounting levels of carbon dioxide in the atmosphere.
So why were the grasshoppers faring increasingly worse?
“We thought that this is a pretty nice habitat for grasshoppers,” she said.
The insects dwell on the Konza Long-Term Ecological Research site. Their home sat in preserve, shielded from development, from farming, from just about everything people do to the planet.
“It doesn’t have a lot of the pressures we usually associate with insect decline. Like, there’s no pesticide spraying,” Welti said. “The size of the habitat is not shrinking. It’s the big natural reserve.”
And yet the numbers showed an alarming decline — nearly 2% a year for about a quarter century.
“It’s like compound interest,” said Michael Kaspari, a research professor at the University of Oklahoma who advised Welti on the paper. “You add that up over 25 years and we’re talking about a significant decline in one of the most important insects on the prairie.”
Even this treasured research site — part of a worldwide network aimed at studying a biological baseline — shares the atmosphere with the rest of the Earth.
Welti and her research team found that all those human-boosted levels of carbon dioxide in the air changed the grass. Bigger leaves, sure, but all that volume diluted the nutrients grasshoppers need to thrive.
Basically, climate change had converted the grasshopper’s staple into insect junk food.
“That was a surprise for me,” Welti said. “But thinking more about it and knowing about grasshoppers and how sensitive they are to these plant nutrients, it makes a lot of sense.”
A normal amount of grasshoppers on the prairie can eat as much grass as a herd of cattle. Grasshoppers are a huge part of the tallgrass ecosystem. But they’re also limited. They really just eat the grass, so when it changes, it can have a huge impact.
To figure out just what was going on, Welti went back to the Konza research station to take a deeper look. Researchers there have tens of thousands of grass samples from the last 40 years.
