You may be catching worms to present to your grade school biology class, or you may need bait for your fishing trip. Either way, you probably want an easier way to extract them from the soil than using a shovel.
Digging holes in the garden isn't the most efficient way to find worms, it defaces the soil and it doesn't reach large, deep-diving earthworms, unless you're prepared to dig 2-foot-deep holes. An easier method for getting worms out of the ground is to use a vermifluge, a solution that will flush the worms out.
A solution of mustard powder and water makes a great vermifluge. Pour it in a section of the garden, wait a few minutes and pick up the worms as they surface to escape the irritating effects of mustard on their skin.
How Does Mustard Work and Does It Hurt the Worms?
Mustard irritates the skin of the earthworms and causes discomfort, but it produces no long-term problems for the worms. You should wet down the worms after catching them, because their skin needs moisture to help them breathe, and the water will wash off any residual mustard.
The worms that you don't pick up will simply end up crawling to a different part of the lawn or garden, and the mustard will eventually wear off.
The irritant in mustard is the oil allyl isothiocyanate, which is the chemical that makes mustard, wasabi, horseradish and radishes taste hot. The worms feel the same intense discomfort that you do when you put too much wasabi on your sushi, but it's momentary.
If it wasn't, no one would ever eat wasabi with their sushi. Allyl isothiocyanate isn't the only chemical you can use as a vermifluge, but alternatives such as potassium permanganate or formalin are harmful, and they may not be as effective.
Procedure for Getting Worms Out of the Ground
A vermifluge works best if you use it in a section of the garden rather than pouring it everywhere. This also gives worms you don't catch a way to escape the irritation.
Mark out a space about a square foot in area. The soil should be rich and fairly dry.
If it's too wet, the solution won't sink in, and you won't catch larger, deep-burrowing worms.
Mix 2 liters or 2 quarts of water with 20 grams (3/4 ounce) of store-bought mustard powder. Don't use table mustard – it isn't hot enough.
Stir until all the powder is dissolved, then slowly pour about half the solution on the soil. As the worms come to surface, pick them up and put them in a collection tray.
Let the worms surface completely before catching them to avoid breaking them when you pick them up.
After you've collected all the worms that surfaced, pour half of the remaining solution into the soil to force deeper-burrowing worms to the surface. Finish off by pouring all the rest of the solution into the soil and catching worms that continue to surface.
Is Mustard Extraction the Same as Worm Grunting?
Worm grunting is a traditional technique for catching worms. It isn't the same as mustard extraction, because it doesn't rely on a chemical solution.
Instead, the worm grunter creates vibrations in the soil by pounding a wood pole into the ground and rubbing it with a strip of metal. The result sounds weird to human ears, and it must sound even weirder to worms, because they come to the surface when they hear it.
Using this technique, an experienced worm grunter can catch 3,000 to 4,000 worms in a few hours.