Crunching worms, squeaking voles, drumming ants: how scientists are learning to eavesdrop on the sounds of soil (

Until recently, soil had been a relative blank spot for monitoring species abundance. Farmers and gardeners hoping to find out how healthy their soils were had to dig up spadefuls and carry out laborious tests.

Last year, a study found soil was the single most species-rich habitat on Earth, with more than half of all species living in it. But only a fraction have been identified, and most are too small to see. Soundscapes are becoming an increasingly popular way of monitoring wildlife abundance, above ground, beneath the earth and underwater.