Soil Ecology
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Soil Organisms and Species

Earthworm (Lumbricus terrestris)

The soil is also home to many different types of living things. An individual living thing is known as an organism, and all organisms of the same type are known as a species. A species is defined as all organisms that can reproduce with one another and produce fertile offspring.

There are billions of earthworms in the world - each earthworm is an individual organism, but they are all members of the earthworm species.

Because scientists around the world all work together, and these scientists speak many languages, they cannot call earthworms by their common name "earthworm." Instead, scientists all over the world use a two-word name that comes from Latin to identify a species. For example, the common earthworm (pictured to the right) is known to scientists as Lumbricus terrestris.

An important measure of the health of an ecosystem such as soil is the variety of species that live in that ecosystem. The variety of species living in any natural environment is known as that environment's biodiversity. Soil environments have some of the greatest biodiversities on Earth.


There are many ways to define biodiversity. The simplest way is to count the number of species in an ecosystem, and the number of individual organisms of each species. But this is a challenge, because many species of soil organisms have never been identified - there are too many species and too few soil ecologists!

The many species that live in the soil range in size from tiny one celled bacteria, algae, fungi, and protozoa to more complex organisms like earthworms, insects, small vertebrates, and plants. The table below shows six of the many species that live in the soil in the eastern United States.

Potato bug
(Porcellio scaber)
(Armadillidium nasatum)
Common woodlouse
(Oniscus asellus)
(Porcellio dilatatus)
(Narceus americanus)
Asian Earthworm
(Amynthas hilgendorfi)

Since there are so many different species in the soil, how do all these creatures live with one another and their environment? What role do these soil organisms play in their ecosystem? To answer these questions, ecologists try use the study methods described on the previous page to understand what organisms need to survive, and what contributions these organisms make to their environment.

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