We all recognize them when they cross our paths. Some of us relish them. For instance, as engineers they are valued because they break down nutrients while aerating and draining the soil, or for fishing we use them for fishing bait as fish and many other animals eat them.
Worldwide, over 6,000 species exist and are quite variable in habits and habitats. Regardless of the species, earthworms are constantly digging burrows into which they carry organic material they have collected. To assist in processing these organics, they churn them into a paste they can then digest, using small grains of sand they ingested as a grinding agent to break up the materials and make them more palatable. Much like a birds crop. Unused components of the ingested materials (i.e. humus) are pooped out in soil-like casts. These casts and the inherent humus are immediately available to plants, to assist in food production and growth, since they yield nitrogen, phosphates and potassium in amounts 5, 7 and 11 times higher respectively than in surrounding soils!
Earthworms move, a lot! As they travel through the soil, they carry these castings and organic material to all depths in the soil, and constantly open channels to allow air to move into the soil and water to drain through it. This behaviour makes them foundational in ensuring soils are healthy and plant growth is productive. Studies show, without earthworms, soil fertility is greatly reduced.
Incredibly abundant, they can be found in large numbers in healthy environments. For example, Rothamsted Research Station in England estimates fertile land can have upwards of 1.75 million earthworms per acre!
Earthworms are hermaphrodites (i.e. individuals carry both male and female sexual reproductive parts). Mating is complex, and essentially earthworms are parthenogenic where young are produced without external fertilization. In some species, they need the stimulus of mating, but in a non-traditional way where embryos are produced without the sharing of sperm. Most mating takes place at night but can also occur on overcast, rainy days.
Once the reproductive activity is complete, a small cocoon is formed and then deposited in the soil. Within this cocoon, the baby worm will develop and emerge after about three weeks. They do not undergo complex developmental stages like butterflies which change from eggs to larvae to pupae to adults, but rather simply emerge as small worms that gradually get bigger. In 60 to 90 days, they too can breed and restart the cycle.
Earthworms can’t see because they don’t have eyes, but they do have photosensitive cells called ‘Light Cells of Hess’ which allow them to sense variations in light intensity and thus changes in the environment. Other sensors can be found over the entire surface of the worm and help it detect changes in temperature, vibration and texture. In the digestive part of the body, different receptors help with taste and smell. So despite being quite primitive, their sensory capabilities are very advanced.
To a degree, earthworms can regenerate lost body segments, but it varies between species and depends on the extent of the damage.
Locomotion is complex, as they don’t have legs, but they rely on muscular contractions to shorten and lengthen their body length, thus moving their body forward with each thrust. Movement through the soil is assisted with mucous they secrete. Incredibly strong, adults can move soil particles 10 times their body weight. In comparison, very young worms can move materials 500 times their body weight, wow!
Most earthworms aren’t very big, averaging less than an inch (2.5 cm) and ranging up to 8-10 inches (20-25 cm), depending on the species. One species of worm from Southeast Asia measures over 3 meters in length!
A recent inconclusive story on CBC is suggesting, non-native earthworms are changing our forests and affecting climate change, due to the speed at which they break down organics.
Interestingly, I tried to confirm if earthworms are native to North America and were unsuccessful. Many sources say absolutely not, while others state, several species are, in fact, native. Regardless, they are an important part of our ecosystem, both from a prey and soil rehabilitation perspective.
Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff online at LinkedIn and Facebook.