They’re dirt-dwelling invertebrates, but, in a sense, they’re the real backbone of Earth’s carbon cycle.
Thousands of species of mites and springtails, living in soil all around the world, provide a crucial service by munching organic matter like fallen leaves and wood, transferring its planet-warming carbon into the ground and releasing nutrients that help new plants grow.
But now, a new analysis that combined data from 38 different studies on the organisms suggests that drought in some parts of the world, often supercharged by climate change, are killing them off at alarming rates.
“It is important to take care of these critters in particular because we know so little about them,” said Ina Schaefer, a soil invertebrate ecology researcher at the University of Göttingen in Germany.
While some of these organisms live deep within the soil, others spend most of their lives scuttling around on the surface. Scientists don’t fully understand exactly how they break down decaying organic matter, but new molecular research shows springtails actually have special genes for the job.
(That’s not their only talent: Some springtails are about the size of a grain of sand and can fling themselves into the air like circus acrobats, spinning up to 500 times per second. Scientists think it could be a way to escape predators.)
Mites and springtails have not been widely studied, despite their importance, but scientists do know that some of the soft-bodied creatures are very sensitive to moisture in their environment.
When the soil dries up during times of aridity they, too, can dry up, shrivel and die. On average, their populations shrink by a whopping 39 percent during long stretches without rain, according to the analysis, which was published this month in Global Change Biology.
And, the more severe the dry spell, the more severe the reduction in their abundance, said Philip Martin, a researcher at the Basque Center for Climate Change in Leioa, Spain, and one of the lead authors of the study. Under extreme conditions, “you’re losing way more than just that 39 percent figure,” Dr. Martin said.
Earlier research has indicated that the abundance of springtail populations is broadly linked to heat. Each degree of Celsius increase in temperature corresponds with a drop of springtail populations by almost 10 percent, according to a 2023 analysis.
“They really do bad,” Gerard Martínez-De León, a doctoral candidate in terrestrial ecology at the University of Bern in Switzerland, said of springtails during heat waves. “If there are very high temperatures for, let’s say, one week, two weeks, one month, this affects them directly. Probably as much as the lack of moisture does.”
Droughts also change and shrink the populations of fungi living in the soil, according to research published in January, which is what springtails predominantly feed on.
Yet, there are a few factors playing in favor of soil dwellers.
Generally, mites do better in heat than springtails, and studies suggest that some springtail species are better than others at withstanding heat and dryness. When times get tough, some invertebrates will move further down into the soil or travel out to more moist spots in their surroundings, say, under a rock. And, others will pick up new diets and tweak their preferences.
And, the effects of climate change aren’t the same the world over. An increased temperature of, say, 4 degrees Celsius and decreased soil moisture by 20 percent will have a different effect on a mid-latitude desert, a high-latitude peatland, or a tropical forest, according to Zoë Lindo, a soil biodiversity expert at the University of Western Ontario. Her research has shown that different combinations of warming and wetting, and drying and cooling, affect soil communities differently.
“Many different components interact in ways that are constantly changing,” Dr. Lindo said, and these all affect “the richness, abundance, and composition of soil biodiversity all at once.”
It’s also important to note that, while some areas will experience more droughts as the climate changes, others are expected to see more abundant rainfall.
There are more than 12,000 known species of oribatid mites and 9,000-something species of springtails, but scientists think those numbers might represent just 20 percent of their global species richness.
That lack of information might be the biggest problem facing soil invertebrates. More than half of the planet’s biodiversity is somewhere below our feet. In addition to mites, which are arachnids, and springtails, which used to be classified as insects but now have their own group called collembola, there are about 430 million species of bacteria, almost 6 million species of fungi and roughly 20,000 kinds of worms down in the dirt.
But there’s a dearth of data for several large chunks of the planet. Because we don’t fully understand how each species is contributing to the ecosystem, we don’t know what might happen if we lose them.
“Soil has been like a black box,” said Leticia Pérez-Izquierdo, a terrestrial ecosystems researcher at the Basque Center for Climate Change in Spain who worked on this month’s study. “And we’re now starting to open it.”