We are familiar with herbivores that are plant eating and carnivores that eat animals. There is yet another group of organisms that rely on dead organic matter. They are called saprotrophs. These are of two kinds – decomposers (Bacteria, fungi) and detritivores (animal consumers of dead matter). Both decomposers and detritivores are specialists in causing decay of non living organic matter. The decay results from combined activities of both these group of organisms with widely different structures, forms and feeding habits.
Detritivores are scavengers that feed on dead plants as well as animal wastes like dung or feces of herbivores. They are responsible for recycling the nutrients of the soil. Without them, the dead plants and animals would take more time to decay. They help in speeding up the process and giving back the nutrients to the soil. Both detritivores and decomposers are less active when the temperatures are low, aeration is poor and the soil is dry. Structure and porosity of the soil is very important because these organisms must find enough space to swim, creep, grow or force their way through the medium in which their food is dispersed.
The rate at which the organic matter decomposes depends on its bio chemical composition and on availability of mineral nutrients in the environment. Major organic components that are present in the dead leaves and wood are lignin and cellulose. The detritivores find it difficult to digest these two organic substances on their own. They depend on the microbes to digest them.
The only distinction between the group of organisms constituting the herbivores, carnivores, parasites etc and the saprotrophs is that the former group has a control over the rate at which their food is produced. For example, parasites are found on grass, grass is eaten by a deer and deer is eaten by a lion. The act of eating a deer harms the deer’s ability to reproduce more deer.
Earth worms, millipedes, wood lice, dung flies, worms and many other marine creatures are typical examples of detritivores.