Detritivores: Earthworms, Millipedes, and Woodlice at Work

1.1 What is a detritivore?

A detritivore is an animal that swallows bits of dead matter and digests them inside its body. That is how it breaks the matter down. Most are small invertebrates, animals without a backbone. Examples are earthworms, millipedes, woodlice, dung beetles, sea cucumbers and sea stars.

1.2 What is detritus?

Detritus is the loose debris of dead things. It is dead particles of plants and animals, plus the waste that living things leave behind. Fallen leaves are detritus. So are droppings and bits of dead wood.

In the sea, some detritivores feed on floating detritus called marine snow.

1.3 Why does the detritivore matter?

It matters because detritus holds energy and nutrients locked up in things that have already died. Eating it is a major route for recycling both. Without this step, the dead matter would stay locked up.

2.1 How is a detritivore different from a decomposer?

A detritivore swallows its food, but a decomposer does not. Decomposers are bacteria, protists and fungi. They release enzymes onto dead matter and absorb the breakdown products from outside. They never swallow a chunk.

2.2 How is a detritivore different from a scavenger?

A scavenger feeds on whole carcasses, while a detritivore eats small particles. Scavengers eat the bodies of larger dead animals, called carrion. Vultures, hyenas and crows are scavengers, not detritivores.

Source: ScienceABC, Detritivore.

3.1 Are all earthworms the same?

No. Earthworms differ because they live and feed at different depths. Scientists sort them into three groups. The groups are epigeic, endogeic and anecic.

3.2 What does each group do?

• Epigeic (surface) worms live in leaf litter, deadwood, dung and compost. They tend not to make burrows.
• Endogeic (soil) worms live in and feed on the soil. They make horizontal burrows.
• Anecic (deep) worms make permanent vertical burrows. They feed on leaves dragged down from the surface.

A simple memory hook: epigeic stays on top, endogeic stays inside the soil, and anecic links the two.

4.1 What is vermicomposting?

Vermicomposting turns food and garden waste into compost by using earthworms. It works because the waste is both food and bedding for the worms. No soil is needed. For that reason, only surface-dwelling (epigeic) worms can be used.

4.2 Which worm is used?

The red wiggler, Eisenia fetida, is the best-known choice. It is epigeic, so it lives in litter instead of deep soil. IntechOpen lists it among the species tested for vermicomposting.

4.3 Does the government support organic farming?

Yes. India’s Paramparagat Krishi Vikas Yojana (PKVY) pays farmers to adopt organic methods. Support is Rs 31,500 per hectare over three years. Of that, Rs 15,000 is for organic inputs, paid by direct benefit transfer (DBT).

PKVY is open to farmers and institutions with up to two hectares. Farmers join in groups of 20 hectares each.

5.1 Are all earthworms good for soil?

No. Most help soil, but jumping worms harm forests because they eat leaf litter far too fast. Usually, earthworms improve drainage, add air, raise nutrient supply and build soil structure. Jumping worms (genus Amynthas) are the exception.

5.2 Where do jumping worms come from?

They come from eastern Asia and were introduced to North America. They are invasive, meaning they spread where they do not belong. They live and feed near the soil surface instead of deep down.

5.3 Why do they damage forests?

They damage forests because they strip the leaf litter that other life depends on. Oregon State University says they eat two to three times more litter than burrowing worms. Bare soil is left behind.

That bare soil encourages invasive plants and animals. It disrupts native ecosystems.

6.1 Is a woodlouse an insect?

No. A woodlouse is a crustacean, because it belongs to the same group as crabs and lobsters. It is a land animal, but it is more closely related to crabs and shrimps than to land insects. There are around 3,500 species worldwide.

6.2 Why do woodlice stay in damp places?

They stay damp because they breathe through gills. Woodlice need water to respire. They survive with just enough dampness to cover their external gills.

In woodland, they eat dying and decaying plants. They rarely destroy living plants. Rotting leaf litter helps return nutrients to the soil.

6.3 How do millipedes defend themselves?

Many millipedes defend themselves with chemicals made in glands along the body. In the cave millipede Brachydesmus troglobius, glands on both sides of the body segments release a secretion. It is a mixture of five compounds. Hydrogen cyanide was detected in it by a picric acid test.

That test was qualitative. It shows the gas is present. It does not show how much.

7.1 Do dung beetles cut greenhouse gases?

Not on their own, because time does most of the work. A 2020 pasture study tested two beetle species on cattle dung. Time changed gas output two to five times more than beetles did. The authors say beetles cannot cut gases unless they speed up decay faster than time alone.

The beetles still work fast. They took apart dung pats within 2 days. Their effect on gases is the open question.

7.2 How do termites digest wood?

They digest wood with the help of microbes in the gut, because they cannot do it alone. The microbes break cellulose, the main sugar in wood, into short-chain fatty acids. The termite’s cells use those acids as food.

Methane is a major by-product of this breakdown. Termites are a large source of methane in the air.

8.1 What does a sea cucumber do?

A sea cucumber cleans the seafloor because it swallows sediment and digests what little food is in it. It then passes out the undigested material. NOAA says this helps spread and aerate the sediment. That makes it healthier for other animals.

8.2 Are sea cucumbers at risk?

Yes. A 2014 Southern Cross University report cited the latest Red List of the International Union for Conservation of Nature (IUCN). It classed sixteen sea cucumber species as threatened with extinction.

8.3 What does a fiddler crab eat?

A fiddler crab eats algae, bacteria, fungus and detritus. The detritus is dead and decaying plant and animal matter. The male has one oversized claw. He waves it in a fiddling motion to attract a female.

9.1 What did UPSC ask?

9.2 Why were jellyfish and seahorses wrong?

They were wrong because both catch live food. A box jellyfish stuns or kills prey such as fish and shrimp. A moon jelly eats zooplankton, tiny drifting animals. Seahorses wait for krill, copepods and fish larvae to drift by.

Seahorses have no teeth and no stomach. They suck up plankton almost continually. None of this is detritus feeding.

9.3 Which mix-ups come up?

• Habitat. The sea does not decide it. Sea cucumbers are detritivores. Jellyfish are not.
• Insect. A woodlouse is a crustacean.
• Decomposer. Fungi and bacteria absorb food. They do not swallow it.
• Scavenger. Vultures eat carcasses. They are not detritivores.