Getting personal with earthworms

I am not sure how our summer students explain their summer job to friends and family. For the last few years we start them off with earthworm counts on the cover crop plots. It is a dirty and a bit time consuming job but quickly shows the impact different management practices have on soil life. Every year the students ask questions prompting me to go back to the literature for some wormy facts.

'Thumbs up' to manure 'Thumbs down to salts

Applying manure or other organic amendments can increase earthworm numbers quickly, causing numbers to increase 2 to 3 times in one season. Earthworms are sensitive to high levels of ammonia and salts, so some liquid manure can reduce populations but only for a short period of time.

Intestines of the earth

That's what Aristotle called them. Darwin, with a bit more Victorian restraint, referred to them as Nature's plow. Research has shown that in healthy, active soils about 5% of a soil's A horizon, basically the topsoil, passes through the gut of worms per year. So they were right.

Casting sculptors

Earthworm pass soil through their bodies leaving behind casts. Casts are soil enriched with nutrients and bacteria. Casts do not look the same. They can be globular, a paste like slurry, tall vertical columns or heaps, and a form that appears like pellets.

It's all about eating

Earthworms are omnivores, meaning they eat a variety of things from plant residues to occasionally animal remains. Dew worms can also withstand considerable starvation and water loss of up to 70 % of body weight; so some of those dried worms on the sidewalk may come back.

And sex

Spring is a busy time for most earthworms. While they are hermaphrodites, most require another worm to fertilize the eggs. You will often see dew worms stretched out on the soil surface. They secrete a mucous sheath that holds them tightly together. After they both release sperm they will secrete some more mucous to form the egg cocoon. The dew worm reproduces slowly usually laying only 1 to 2 eggs at a time for a total of maybe 10 in a year. In the spring, if you come across tiny worms that are white and only a few millimeters in length - these are probably newly hatched earthworms.

How old do they get?

Earthworms have the potential for a very long life cycle of 10 to 12 years but in the field they tend only live 1 to 2 seasons due to predators and other things like tillage implements.

Figure 1. Plant roots using worm channels

Figure 1. Plant roots using worm channels

Figure 2. Worm channel lined with plant residue

Figure 2. Worm channel lined with plant residue

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