You’re going to sample two areas - one open area (agriculture, garden, etc.) and one forested area. Find a place to sample and mark out a spot 25 cm x 25 cm. You will use three methods to sample for earthworms: 1) midden counts, 2) hand-sorting, and 3) mustard extraction
Do a midden count first. Deep burrowing earthworms form piles of feces around the openings to their burrow holes. These piles are called middens and they are normally 2 to 5 cm in diameter and 1 to 2 cm high. In the center of the pile, there will be a burrow hole. Normally only one deep burrowing earthworm lives in each burrow hole, so counting the middens can give a good estimate of the number of earthworms in an area.
Next, you will hand-sort the soil to look for earthworms. Use a trowel or shovel to dig a 25 x 25 cm hole and put the soil on a garbage bag. The hole should be 10 cm deep. If you are with a partner, one person can start sorting through the soil from the hole while the other does the mustard extraction. (If you are by yourself, do the mustard extraction next and sort through the soil from the hole afterwards.) Pick up a handful of soil from the pile on your garbage bag and look through it for worms. If you find a worm, put it in a container. Use different containers for the earthworms you collect from hand-sorting and the earthworms you collect from mustard extraction. Discard your handful of soil to the side after looking and do this until you have looked through all of the soil.
After digging your hole, you will use mustard to find deeper dwelling earthworms. The mustard acts as an irritant to the skin of the earthworms, but it doesn’t hurt them. Here is how to do a mustard extraction:
- Add 20 g of mustard powder to 2 L of water. Make sure you shake the bottle to mix it up!
- Pour half of the mustard solution on the ground in your plot.
- Set a timer for 5 min. During this time, collect any earthworms that come up into a container (a different one than the one for the hand-sorting). It’s important to wait for the earthworms to come almost all the way out before you try to pick them up so that you don’t break them.
- After your timer goes off, add the other half of the mustard water to the plot and set your timer for another 5 min. Collect any worms that come up during this time.
Once you have finished the mustard extraction and hand-sorting, add a bit of water to the container to wash off the earthworms. Next, determine the number of adults and juveniles and the number of earthworms in each functional group.