A Fascinating Phenomenon

In the heart of Florida's Apalachicola National Forest, a scene of peculiar enchantment unfolds. A master summoner, sliding a metal strip over a wooden stake, produces deep croaking noises that reverberate through the area. Astonishingly, hundreds of earthworms begin emerging from the soil as if under a spell. This practice, known as worm grunting, worm charming, or fiddling, has been a tradition for over a century. While its existence has long been known, the true mechanics behind it have remained a mystery until recently.

The sight of worms collectively undertaking an underground exodus seems implausible, considering the vulnerability it poses to them. Why would surfacing be worth the risk? Over the years, imaginative hypotheses have been proposed to explain this phenomenon.

One theory suggested that worms were bewitched by the noise, akin to the rats lured by the Pied Piper in medieval legends. Although this notion sounds intriguing, the actual process of enchantment remains unclear.

Another hypothesis posited that worm grunting tickled the worms' bodies, compelling them to emerge to alleviate the irritation. While whimsical, this theory fails to account for the fact that worm grunting causes vibrations on the ground's surface. If worms were seeking to evade these vibrations, wouldn't they burrow deeper instead?

Perhaps the most popular hypothesis suggested that worm grunting mimicked the sound of falling rain, causing worms to flee to avoid drowning. In 2008, biologist Kenneth Catania conducted an experiment to test this idea. He set up three arenas filled with soil, each containing 300 earthworms of a large species found in the Florida Panhandle. After an hour of rainfall, water accumulated on the surface, yet only two earthworms emerged. The majority remained buried and unharmed. Thus, this hypothesis, like the containers, failed to hold water.

Inspired by Charles Darwin's observations, Catania embarked on a different line of investigation. In Darwin's final work, "The Formation of Vegetable Mould, Through the Action of Worms, with Observations on their Habits," he noted that worms sometimes left their burrows when the ground trembled, suggesting they might be fleeing from moles. Catania decided to test this hypothesis himself.

His research revealed that Eastern moles possessed remarkable tracking abilities, consuming their weight in worms daily, and were abundant in the Florida Panhandle. When Catania introduced a single mole into the arenas filled with worms and soil, approximately 30% of the worms crawled to the surface within the first hour. This marked a stark contrast to the control and rain trials. Moreover, when he compared the vibrations produced by worm grunters and moles digging, their frequencies substantially overlapped. This discovery provided a breakthrough.

Over hundreds of thousands of years, these earthworms had evolved a behavior that allowed them to evade a top predator. Aboveground, they were safe from the moles that predominantly remained underground. However, when humans arrived, they inadvertently capitalized on this behavior. Interestingly, humans aren't the only ones exploiting it. Herring gulls and wood turtles also drum their feet on the earth to summon worms.

But why does this behavior persist? Scientists posit that it is beneficial for a prey species to maintain adaptations against a more frequent predator, even if it makes them more vulnerable to rarer ones. Many insects employ flight as a defense mechanism, but painted redstarts have taken advantage of this by flaunting their colorful tail and wing feathers, luring insects into flight and catching them in the process. Thus, the prey species' response endures simply because it proves advantageous most of the time.

For over a century, people in the southern United States, the United Kingdom, and other regions have unknowingly tapped into the worm's escape response. In 2009, a 10-year-old British girl set the world record for "most worms charmed" by wiggling a fork in the ground and striking it with a stick, coaxing 567 worms to surface in just 30 minutes.

Undeniably, worm grunting is a charming and fascinating phenomenon that sheds light on the intricate interactions between species and their adaptive behaviors.

Henrik Leandro