Earthworms may not summon the excitement that animals like crocodiles and cuttlefish do, but their contribution to the ecosystems of the world is significant. Earthworms are often called ‘ecosystem engineers’1 due to the fact that they drastically alter the chemical, physical, and biological properties of the soil profile.
Recycling organic material to make castings:
Earthworms break down and decompose most organic material. People all over the world use worms for their compost bins but earthworms do the same thing in the soil everywhere else. Consuming roughly a third of their body weight every day, earthworms primarily eat the soil they live in, which is full of nutrition from decaying roots and leaves. Earthworms also eat animal manures, nematodes, protozoans, rotifers, bacteria, fungi, all decaying plant matter, and the decomposing remains of other animals. Worms use their strong mouth muscles to eat and burrow through the soil. As they burrow, they actually swallow all of the soil that is in front of them, allowing it to pass through their system and to become ‘worm castings’ (worm poop). Worm castings are the richest natural fertilizer known to humans. A tablespoon of pure worm castings provides enough nutrition to grow a six-inch potted plant for over two months2!
Improving soil structure and increasing nutrients in soil:
As earthworms burrow through the soil, their trails serve as pours in the soil, changing its structure. These pours aerate the soil, enhancing plant root penetration, and can increase the water infiltration rates up to ten-fold. With more water infiltrating the soil, more nutrients are brought down to the plant roots. Earthworms incorporate organic materials into the soil and unlock the nutrients inside dead organisms and plant matter by eating them. Nutrients such as nitrogen, potassium, and phosphorus are more available to plants after moving through the digestive tracks of earthworms and becoming castings. USDA testing has indicated that earthworm castings carry approximately 8 times the amount of nitrogen, potassium, and phosphorus as the pre-digested soil does3.
Types of earthworms:
More than 4,400 species of earthworms have been discovered on earth. Fortunately, they are all categorized into one of three groups: endogeic, anecic, and epigeic3.
Endogeic worms can usually be found deeper in the soil, building complex horizontal burrow systems. These worms are seldom seen close to the surface but spend their lives in their burrow systems where they feed on nutrients in the mineral horizon and bits of decayed organic matter. These worms are not composting worms3.
Anecic earthworms construct semi-permanent vertical burrow systems that extend from the soil surface all the way down to the mineral layer where endogeic worms are found. Anecic earthworms eat detritus by pulling the undissolved organic matter down to their burrows. These earthworms usually have a flattened tail covered with small hairs called setae that help them to grip the burrow wall to avoid being easily pulled out of the ground by predators. These worms are not composting worms3.
Epigeic earthworms are the most famous type of earthworm and are the type of worms used for composting. These worms form no semi-permanent burrows and live on the soil surface as well as the upper most mineral layer. Epigeic worms feed on detritus and are highly adaptable to the rapidly changing environment of the surface world. Not only are these earthworms tolerant of a sweeping range of environmental conditions, but they are also ravenous eaters and cope well in a densely populated environment3.