How do worms dig?

These fleshy creatures perform an impressive physical feat to wiggle their limbless bodies through the soil

(Image credit: Magyar/ Pixabay)

As the soft, squishy, pink things you first encounter when you’re playing outside as a kid, worms appear extremely fragile. With a soft outer skin and little protection, when you first saw them bury themselves out of sight and into the ground you may have wondered how they managed it. And how can they possibly navigate these depths without any eyes or ears?

When worms dig they are moving a stream of soil. Consuming the loam as they roam, this soil passes through their elongated bodies before being excreted behind them in their wake. Digesting organic matter and leaves as food, they also return nutrients to the soil as they travel.

In a world of darkness, the only method they have to survive the continuous threats of bird beaks, hungry moles and other predators is to feel their way through. Nerves in their bodies can detect light and vibrations as they manoeuvre, and their bodies move in response.

We only get to see worms’ movements for a small fraction of their lives on the odd occasion they surface, so what magic are they working when out of sight and in their element?

Digging anatomy

(Image credit: sandrakula/ Pixabay)

  • Muscular mouths:  Worms’ mouths are so strong they can use them to pull leaves into the ground.
  • Streamlined head: The head is pointed, helping them push through soil. This end of their body is also slightly firmer, which helps to move the earth aside as they push through small crevices.
  • Hairy grips: To ensure that the worm doesn’t stretch in both directions at the same time, moving nowhere, tiny hairs called setae attach to the soil. These take it in turns to grip the soil from the front and back.
  • Vibration sensing: Danger often comes from above. For a blind earthworm, feeling the sensitive vibrations using these nerves can help them to navigate beneath the soil to safer areas.
  • Circular muscles: These outer muscles are responsible for initiating the worm’s movement through the earth, by contrating.
  • Inner muscles: Contractions of the outer body cause these longitudinal muscles to lengthen. Stretching and shrinking in time with these contractions, the worm’s head is able to move further along the soil and the tail follows.
  • Intestinal breakdown: Making up over two-yhirds of the worm’s body, the intestine is responsible for breaking down food. Leftover soil and organic matter continue to travel down the length of the worm and are released in the form of castings. This waste product is high in nutrients and helps fertilise the soil behind it as it moves.

This article was originally published in How It Works issue 136

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