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.
Worms are fun
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.
Earthworm anatomy
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.
Epigeic, endogeic, and anecic earthworms.
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.
Text Sources
Student Investigations in Agro-Ecology 
Nice! I really like how the information is very organized, so if somebody wants to find out about something specific, they can find it with ease.
You mention that “earthworm castings carry approximately 8 times the amount of nitrogen, potassium, and phosphorus as the pre-digested soil does,” but do you know where the extra nutrients come from? Surely they don’t magically appear inside the worm and mix with the castings!
“As earthworms burrow through the soil, their trails serve as pours in the soil.” Here, do you mean “pores”? If you don’t, then I’d like to know more about what you mean.
I really enjoyed reading this post. You did a great job organizing this information into easy to read and interesting sections. The pictures are very specific and respond well to the text around them. You state that, “Worm castings are the richest natural fertilizer known to humans.” What plants are most positively effected by worm castings? Are there any plants that do not respond to worm castings? You also state that,
“A tablespoon of pure worm castings provides enough nutrition to grow a six-inch potted plant for over two months!” This is a very interesting and key point! If I were you, I might add the amount of worm castings used to produce a whole yield of plants.
Another informative factor you add in is the difference of horizontal burrow systems and vertical burrow systems between the two categories of Endogeic and Anecic worms. You explain that the burrowing allows aeration of the soil, enhancement of plant root penetration and the increasing of water infiltration. Based off the vertical and horizontal burrowing, is there one that is more effective than the other? Are they both of the same effect? If one is more productive for different types of produce than the other, you should explain in further detail the different benefits of each.
Overall, this post was very successful and interesting. Great job!
Gabby:
Thank you for your comment! The worm’s digestive track works as a filter, thus getting rid of the excess soil matter and bringing out the nutrients. Also thank you for the correction, I meant to say ‘pores’.
Anika:
Unlike animal manure and artificial fertilizers, worm castings are absorbed easily and immediately by plants. This makes it useful to any plant that benefits from fertilizer. As for vertical and horizontal burrows, one is not better that the other as they are both necessary for the soil structure and ecosystem.
Very informative! My only concern is that you include that the worm species that are most productive in vermicomposting is the Red Wiggler or Manure Worm – Esienia fetida http://en.wikipedia.org/wiki/Eisenia_fetida – these are much different than other earth worms.