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Serving Northern St. Louis County, Minnesota

Spittlebug coloration signals a changing climate

Marshall Helmberger
Posted 3/22/23

Hypothesis made, hypothesis confirmed.That was the conclusion of an admittedly obscure study that happened to connect to the North Country, and on which we had reported on back in August 2021. The …

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Spittlebug coloration signals a changing climate


Hypothesis made, hypothesis confirmed.
That was the conclusion of an admittedly obscure study that happened to connect to the North Country, and on which we had reported on back in August 2021. The two researchers behind the study were a New York couple, Vinton Thompson and his wife Ruth Moscovitch and they had traveled to our area that summer in order to sample our spittlebug population.
Spittlebugs, for those who don’t know are those smallish insects that we usually only detect from the presence of a marble-sized blob of whitish spittle on tall grasses and wildflowers.
Vinton, who is a retired college president and still keeps active as a research associate with the American Museum of Natural History in New York City, had traveled through our area once before on an insect-collecting tour as a young man in the 1970s. His analysis had confirmed that our region had the highest percentage of dark morph spittlebugs in all of North America. At the time, he hypothesized that the dark form of the spittlebug would be most abundant in the coldest portions of the insect’s range, since the dark color would help the insect absorb more sunlight and stay warmer during the sometimes-cool North Country summers.
And, so, he was back nearly 50 years later to take another sample to further test the latest permutation of his hypothesis. The couple suspected that the warming climate would lead to a reduction in the percentage of dark morph spittlebugs. They even calculated how much they might decline based on the amount of warming.
I interviewed Thompson and Moscovitch back in 2021, while they were sampling insects at the Hwy. 169 wayside rest in Soudan. Since the conditions had changed significantly there (mowed lawn versus an untamed field), they ended up collecting their relevant sample at the intersection of Junction Road and the Taconite Trail. They took samples in other places in northeastern Minnesota where Thompson had visited in the 1970s, including Isabella, Tofte, and Ilgen City down on the North Shore. I asked that they send their results once they had completed their study, which they did recently. It was published late last year in the journal Entomologica Americana, and it largely confirmed their hypothesis, although I will spare you the fine points, which include percentages of several different spittlebug morphs, regression analysis, etc. We’re just not going there today. Count yourself lucky.
Thompson gave me the shorter version in an email last month. “The headline is that yes indeed the bugs do provide evidence for real effects of local climate warming,” he wrote. “To be honest, when I looked at the NOAA [National Oceanic and Atmospheric Administration] data it was disconcerting to see how much the temperature had gone up in the area— 2.7 degrees C (=4.86 degrees F) is a lot of warming!”
And as the area warmed, the percentage of some of the darker morphs in the population declined, at rates very close to what Thompson had predicted. Does it prove the change was due to climate change? Not exactly. This shows a predicted trend that correlates very closely with the increase in temperatures in our region.
By itself, it’s just one small piece of a very large puzzle that thousands of scientists are working on every day to understand, namely how is the warming climate affecting the incredible diversity of life all around us? It’s a question that will occupy scientists for decades, probably even centuries, to come.