They are invertebrates that live in the soil, but in a sense they are the true pillars of the Earth's carbon cycle.
Thousands of species of mites and springtails live in soils around the world, feeding on organic matter such as fallen leaves and wood, making a vital contribution to soil health by releasing carbon that contributes to global warming into the ground and releasing nutrients that help new plants grow.
But now a new analysis combining data from 38 different studies on the organisms suggests that droughts in some parts of the world, often made worse by climate change, are killing these creatures at alarming rates.
“It's important to pay particular attention to these creatures because we know so little about them,” says Ina Schäfer, a soil invertebrate ecology researcher at the University of Göttingen in Germany.
Some of these creatures live deep in the soil, while others spend most of their lives roaming the surface. Scientists still don't fully understand how these creatures break down decaying organic matter, but a new molecular study shows that springtails actually have special genes for the job.
(And that's not their only talent: Some springtails, no bigger than a grain of sand, can leap into the air like circus performers and spin up to 500 times a second. Scientists think this may be a way to evade predators.)
Despite their importance, mites and springtails have not been widely studied, but scientists know that some mollusks are highly sensitive to moisture in the environment.
When soil dries out during dry periods, plants wither, wilt, and die. During extended periods without rain, plant populations decline by a staggering 39 percent, on average, according to an analysis published this month in the journal Global Change Biology.
And the more severe the drought, the more severe the decline in fish populations, said Philippe Martin, a researcher at the Basque Climate Change Center in Leioa, Spain, and one of the study's lead authors. “In extreme situations, we're losing a lot more fish than the 39 percent figure,” Dr. Martin said.
Previous studies have suggested that springtail abundance is loosely linked to heat: For every 1 degree Celsius rise in temperature, springtail populations decline by about 10 percent, according to a 2023 analysis.
“It's a really bad situation,” Gerardo Martinez de Leon, a doctoral student in terrestrial ecology at the University of Bern in Switzerland, said of the springtails during heatwaves. “If you have very high temperatures for, say, a week, two weeks, a month, they're directly affected, probably as much as a lack of water.”
A study published in January found that drought also alters and reduces the populations of soil-dwelling fungi, which are the main food source for springtails.
However, there are also several factors that favor soil organisms.
Mites are generally more tolerant of heat than springtails, and research suggests that some springtail species are more tolerant of heat and dryness than others. When conditions get tough, some invertebrates burrow deeper into the soil or move to moister areas around them, such as under rocks. Others change their food preferences as they discover new foods.
And the effects of climate change will not be the same around the world. For example, a 4°C rise in temperature and a 20 percent decrease in soil moisture will affect mid-latitude deserts, high-latitude peatlands, and tropical forests differently, says Zoe Lind, a soil biodiversity expert at the University of Western Ontario. Her research has found that different combinations of warming and wetting, drying and cooling, will have different effects on soil communities.
“Different factors are constantly changing and interacting, all of which simultaneously affect the richness, abundance and composition of soil biodiversity,” Dr Lind said.
It is also important to note that as the climate changes, some regions are expected to experience more drought while others will experience more rainfall.
More than 12,000 species of oribatid mites and 9,000 species of springtails are known, but scientists believe these numbers represent only 20 percent of the Earth's species richness.
Lack of information may be the biggest problem facing soil invertebrates. More than half of the planet's biodiversity lives beneath our feet. In addition to arachnid mites and springtails, once classified as insects but now in their own group called Collembola, soil harbors some 430 million species of bacteria, 6 million species of fungi, and 20,000 species of earthworms.
But we lack data for some large regions of the planet. We don't fully understand how each species contributes to ecosystems, and we don't know what would happen if we lost them.
“Soil has been like a black box,” said Leticia Pérez Izquierdo, a terrestrial ecosystem researcher at the Basque Country Climate Change Center in Spain, who worked on this month's study, “and we're now starting to open it.”