Detritivores are organisms that survive by consuming decaying organic material, known as detritus. They are typically animals, although some fungi are sometimes classed as detritivores. These organisms play a vital role in a variety of different ecosystems, helping to break down dead matter and release the nutrients stored within it for use my other organims.
In ecology, the terms "detritivore" and "decomposer" are often used interchangeably. These two types of organism do play similar roles in the ecosystem, but they are not exactly identical. Decomposers, rather than ingesting dead organic matter as detritivores do, absorb nutrients on a molecular scale. Similarly, although scavengers play a similar role and some ecologists may include the two types of organism in a discussion for the sake of simplicity, scavengers and detritivores operate on a different scale, with scavengers generally being larger organisms which consume larger amounts of organic matter. A detritivore might feed on the droppings of scavengers or on the parts of carcasses left behind.
The role of this type of organism in the nutrient cycle is to consume dead organic material such as carcasses, fallen leaves, dead plants, animal droppings, and shed skins. Having consumed the material, the organism then excretes or egests waste. This waste contains nutrients which are thus returned to the soil, facilitating new plant growth, or made easier for other organisms to consume. By breaking down dead matter into smaller pieces, detritivores speed up the process of decomposition. The greater surface area of processed waste compared to a dead organism makes it easier for decomposers such as bacteria and fungi to complete the nutrient cycle, breaking up these last remains at a molecular level.
Detritivores make up a significant part of most ecosystems. In many biomes, detritivores make up half of the biomass, excluding plants and bacteria. Common species of detritivore include earthworms, slugs and many species of insect such as flies. Marine detritivores include crabs, sea stars and many species of fish and worm.
One of the most ubiquitous terrestrial species of detritivore is Armadillidium vulgare, also known as the woodlouse or pillbug. This small animal is actually a crustacean of the Isopod order, not an insect. Pillbugs typically consume dead vegetable matter such as fallen leaves or refuse. When pillbugs overpopulate, however, they will sometimes feed on living plants, including cultivated plants, which leads humans to regard them as pests. Although primarily detritivores, pillbugs, like many organisms, can change their behavior as a response to changing circumstances.