Soil structure
Earthworms have been called ‘ecosystem engineers’.
Much like human engineers, earthworms change the structure of their environments. Different types of earthworms can make both horizontal and vertical burrows, some of which can be very deep in soils.
These burrows create pores through which oxygen and water can enter and carbon dioxide can leave the soil.Earthworm casts (their faeces) are also very important in soils and are responsible for some of the fine crumb structure of soils.
Decomposition and soil organic matter
Earthworms play an important role in breaking down dead organic matter in a process known as decomposition. This is what the earthworms living in your compost bin are doing and earthworms living in soils also decompose organic matter. Decomposition releases nutrients locked up in dead plants and animals and makes them available for use by living plants. Earthworms do this by eating organic matter and breaking it down into smaller pieces allowing bacteria and fungi to feed on it and release the nutrients.
Earthworms are also responsible for mixing soil layers and incorporating organic matter into the soil. Charles Darwin referred to earthworms as ‘nature’s ploughs’ because of this mixing of soil and organic matter. This mixing improves the fertility of the soil by allowing the organic matter to be dispersed through the soil and the nutrients held in it to become available to bacteria, fungi and plants.
Bacteria and fungi
Earthworms have a positive effect on bacteria and fungi in soils. Where earthworms are present there are more bacteria and fungi and they are more active. This is important as bacteria and fungi are key in releasing nutrients from organic matter and making them available to plants. They are also an important source of food in their own right for many other animals that live in soils.
Scientific classification
Kingdom: Animalia
Phylum: Annelida
Class: Oligochaeta
Subclass: Haplotaxida
Order: Megadrilacea
Suborder: Lumbricina + Moniligastrida
NODC v. 8.0, 1996[1]
An earthworm is a tube-shaped, segmented animal that is commonly found living in soil. Its digestive system runs straight through its body, it conducts respiration through the cuticle covering its skin, and it has a simple, closed blood circulatory system. Earthworms are hermaphrodites--each individual carries both male and female sex organs. As an invertebrate it lacks a skeleton, but an earthworm maintains its structure with fluid-filled chambers functioning like a hydro-skeleton.
"Earthworm" is the common name for the largest members of Oligochaeta (which is either a class or subclass depending on the author) in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female. Theoretical cladistic studies have placed them instead in the suborder Lumbricina of the order Haplotaxida, but this may again soon change. Folk names for the earthworm include "dew-worm", "Rainworm", "night crawler" and "angleworm" (due to its use as fishing bait).
Larger terrestrial earthworms are also called megadriles (or big worms), as opposed to the microdriles (or small worms) in the semi-aquatic families Tubificidae, Lumbriculidae, and Enchytraeidae, among others. The megadriles are characterized by having a distinct clitellum (which is more extensive than that of microdriles) and a vascular system with true capillaries.
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