There is a confounding mystery wrapped up in the tiny turds of two different types of earthworms, and the secrets locked inside are influencing climate change around the world.

Scientists say some earthworm species are potentially speeding up climate change by feeding on leaves, then pooping out a mix that’s fodder to tiny microbes and fungi that spew carbon into the atmosphere. By contrast, other worms are helping lock carbon in soil.

Canada is ground zero for this paradox. Earthworm populations are growing as warmer temperatures allow the invertebrates to move farther north than ever before.

And no one knows exactly how much carbon they are helping release into the atmosphere.