How the Wolf Spider’s Diet May Help Keep the Arctic Cool

Unlike most of its web-weaving relatives, the beady-eyed, fast-moving wolf spider prefers to stalk its prey. Sometimes the arachnid tracks down and pounces on its ground-dwelling victims; other times, it stages an ambush, lying in wait until the prey ambles past.

In the Arctic, wolf spiders—which, in terms of pure biomass, outweigh the region’s gray wolves by a ratio of at least 80-to-1—typically hunt springtails, primitive wingless insects that subsist on a diet of soil-dwelling fungus. But, according to a new study published in the Proceedings of the National Academy of Sciences, a warming Arctic could shift the spider’s tastes away from springtails, triggering a cycle of events that could serve as a welcome barricade against Arctic climate change.

Science’s Michael Price explains that springtails subsist on a diet of fungi, which consume decomposing plants and release greenhouse gases into the atmosphere. But when wolf spiders keep the springtail population in check, the insects consume less fungus, which triggers faster decomposition of the tundra’s dead plant matter—and more greenhouse gases.

Amanda Koltz, a postdoctoral researcher in biology at Washington University in St. Louis, Missouri, studies climate change’s effect on predator-prey relationships and the wider ecosystem. Armed with the knowledge that global warming likely affects animals’ interactions, she decided to take a closer look at the wolf spider’s response to rising temperatures.

Over the course of two summer seasons, Koltz and her team installed several five-foot-wide miniature ecosystems in the Northern Alaskan tundra. These isolated environments allowed the researchers to control temperatures and closely monitor both the numbers and behavior of the creatures involved. In some of the mini ecosystems, they left temperatures the same, and in others, they installed warming devices that raised the temperature by about 3.5 degrees Fahrenheit to simulate a warming Arctic.

According to National Geographic’s Theresa Machemer, scientists have long known that warming climates could have an outsized effect on wolf spiders. In 2009, researchers reported that rising temperatures meant the roughly half-inch long spider would probably grow larger and produce more offspring, triggering a spike in the species’ population. Higher numbers lead to denser populations, which wolf spiders usually negate by resorting to cannibalism (in addition to eating nearly all insects and spiders smaller than them).

Based on this logic, researchers expected the wolf spiders to attack their springtail prey with added fervor as temperatures rose and spider populations grew. Instead, they found that spiders living in the warmed, densely populated plots largely left the springtails alone, launching a cycle of higher springtail populations, less fungus, slower decomposition and, significantly, less greenhouse gases.

This unlikely turn of events could be the result of the wolf spider’s changing tastes, according to a press release. Rather than preying on springtails, the spiders are hunting “intermediate predators,” such as smaller spiders, and falling prey to infighting amongst their territorial species. But why is still somewhat of a mystery. As Science's Price explains, "[U]ntil researchers know why the wolf spider’s diet is shifting, it will be hard to project the results of a small experiment to the entire region."

Until then, Koltz is optimistic. “Spiders are not going to save us from climate change, but we found that decomposition is slower under warming when there are more wolf spiders present,” she said in the statement. “This suggests that under some circumstances, they could be alleviating some of the effects of warming on carbon losses from the tundra. It’s a good thing.”

Meilan Solly | | READ MORE

Meilan Solly is Smithsonian magazine's associate digital editor, history.