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Earthworm Habitat Studies
General Soil Survey Instructions
There are some simple techniques you can use to describe basic (but important) characteristic of the soils in your site. You can generally conduct one General Soil Survey per site, rather than one at each sample plot. However, if you see a lot of variability in these characteristics across you site, you may want to conduct more than one and then report the average for the site. Use your best judgment.
First, describe what you see on the forest floor.
If there is leaf litter from the previous fall present (usually the leaves are still mostly intact), brush this aside to see what is beneath.
- Are there patches of bare soil visible beneath any fresh the leaf litter? If so, select the category that best describes the average percent of the forest floor that is exposed soil.
- Is there evidence of earthworm activity at the surface? This might include
- burrow openings at the surface. Generally between 2-5mm in diameter. Be sure to look under the surface litter and logs when looking for surface holes of the earthworm burrows
- earthworm cast material (earthworm poop) on the surface of the soil. Earthworm cast material is composed of smooth and rounded clumps of soil which distinguishes it from the more rough, angular or crumb-like surface of soil aggregates that have not been worked by earthworms. Cast material is also usually very dark brown or black in color.
- Nightcrawler middens, are distinctive piles of cast material around the openings to their burrows. These middens are usually about 1-5cm in diameter and 1-3cm in height with a burrow hole (2-4mm in diameter) near the center. The burrow entrances of middens also often have large numbers of leaf petioles or fragments of leaves sticking out of them. These got stuck there as the nightcrawler inhabitants attempt to pull leaves down into their burrows.
- Is there an accumulation of litter from previous years on the forest floor? Litter that has accumulated for years and has formed a "duff layer" will be composed of relatively fresh (whole) leaf litter at the top and older (fragmented) litter below. If a duff layer has developed there will also probably be many plant roots (fresh and old) weaving the whole layer together (see images in the Soil & Forest Floor section). The presence of such a layer suggests that there will probably be few earthworms OR that they have just arrived, since this feature is one of the first things to disappear when earthworms invade a forest.
- If there is a duff layer present, measure it to the nearest centimeter and take some time to dissect it and describe what you find, for example
- Is there evident layering from fresh on top to very decomposed at the bottom?
- Do you see white thread-like roots or fungi throughout the duff layer?
- And any other features you find interesting or intriguing!
Second, use this simple key to determine the average soil texture of your soil.
This tells us a lot about the average conditions earthworms may experience at the site.
Simplified Key to Mineral Soil Texture: adapted from Brewer,R. and M.T. McCann. 1982. Laboratory and Field Methods in Ecology, Saunders College Publishing, Philadelphia, PA
Fill your palm with soil, add water until the soil is fully saturated and then squeeze the soil in your hand until no more water come out. Form moistened soil into a ball as best you can and then follow the key to determine you average soil texture.
| A1 | Soil does not remain in a ball when squeezed | sand |
| A2 | Soil remains in a ball when squeezed | go to B |
| B2 | Squeeze the ball between your thumb and forefinger, attempting to make a ribbon that you push up over your finger. Soil makes no ribbon | loamy sand |
| B2 | Soil makes a ribbon; may be very short (less than ½ inch) | go to C |
| C1 | Ribbon extends less than 1" before breaking | go to D |
| C2 | Ribbon extends 1" or more before breaking | go to E |
| D1 | Add excess water to small amount of soil; soil feels at least slightly gritty | loam or sandy loam |
| D2 | Soil feels smooth | silt loam |
| E1 | Soil makes a ribbon that breaks when 1-2" long; cracks if bent into a ring | go to F |
| E2 | Soil makes a ribbon more than 2" long; doesn't crack when bent into a ring | go to G |
| F1 | Add excess water to small amount of soil; soil feels at least slightly gritty | sandy clay loam or clay loam |
| F2 | Soil feels smooth | silty clay loam or silt |
| G1 | Add excess water to a small amount of soil; soil feels at least slightly gritty | sandy clay or clay |
| G2 | Soil feels smooth | silty clay |