I used to think shrews were just tiny, frantic things that died if they missed a meal.
Turns out, they’re also navigating pitch-black tunnel networks with a sonar system so sophisticated it makes you wonder why we ever thought echolocation was just for bats and dolphins. The common shrew—Sorex araneus, if you’re keeping track—emits ultrasonic clicks at frequencies around 30-60 kHz, well above what we can hear, and listens for the echoes bouncing back from earthworms, beetle larvae, and the tunnel walls themselves. It’s not exactly the same as a bat’s system; shrews don’t have the elaborate facial structures or the massive auditory cortex. But here’s the thing: they don’t need them. Their echolocation is rougher, scrappier, adapted for distances measured in centimeters rather than meters. Research from the Max Planck Institute in 2019 showed that shrews could distinguish between objects just 2 millimeters apart in total darkness, which is frankly unsettling when you consider how small their brains are—roughly the size of a pea, give or take.
How a Metabolism Like a Burning Fuse Shapes Underground Hunting Strategies
Wait—maybe the wildest part isn’t the echolocation itself but why they need it so desperately. Shrews have a metabolic rate so absurdly high they need to eat roughly 80-90% of their body weight every single day. Miss a few meals and they literally starve to death within hours. So hunting can’t be a leisurely affair; it’s frantic, relentless, a biological imperative that never stops screaming. Underground, where most shrews do their hunting, there’s no light filtering through soil and root tangles—just endless, suffocating darkness. Vision is useless. Smell helps, sure, but it’s slow, and shrews don’t have time for slow.
That’s where the clicks come in. A shrew moving through its tunnel system is essentially shouting into the void dozens of times per second, building a real-time acoustic map of everything within a few centimeters. The echoes tell it where the tunnel curves, where the walls narrow, where something soft and wriggly might be hiding. I guess it’s kind of like driving with your headlights on, except the headlights are sound and you’re also possibly having a heart attack from stress because your heart rate is 1,200 beats per minute.
The Messy, Imperfect Science of Measuring What We Can Barely Hear
Honestly, studying shrew echolocation is a nightmare.
For decades, researchers didn’t even know shrews had echolocation because the frequencies are so high and the clicks so faint. Early experiments involved putting shrews in mazes with infrared cameras and sensitive microphones, then watching them navigate obstacles in complete darkness—which they did, flawlessly, while emitting these weird little chirps nobody could hear without equipment. But the data was messy, inconsistent, full of gaps. Some shrews echolocated constantly; others seemed to rely more on touch and smell. Some populations seemed better at it than others, though whether that’s genetic or learned behavior is still up for debate. A 2021 study from the University of Zurich suggested that juvenile shrews actually practice echolocation, refining their click patterns as they mature, which implies it’s not purely instinctual—it’s a skill, honed through trial and error in the dark. And here’s where it gets weird: not all shrew species do it. The water shrew (Neomys fodiens) definitely echolocates, especially when hunting underwater, but other species seem to manage fine without it, relying instead on their whiskers and that absurd sense of smell.
I’ve seen footage of water shrews hunting aquatic insects, and it’s simultaneously elegant and chaotic—this tiny mammal diving into murky pond water, clicking madly, zeroing in on a mayfly larva it can’t possibly see. The clicks get faster as it closes in, a phenomenon called the “terminal buzz” that bats also use right before they snag a moth. The convergent evolution here is striking: two completely different lineages, separated by millions of years, arriving at nearly identical solutions to the same problem.
Which makes you wonder what else is out there, clicking in frequencies we haven’t thought to listen for yet.
