Roundworms or nematodes are the most abundant and ubiquitous multicellular organisms on earth. Between 100,000 and 1,000,000 are believed to exist. Only a small percentage of Australia's species are currently known, with 1000 having been named.

The Challenge

Identifying the most abundant organism in the world

Nematodes are the most abundant and ubiquitous multicellular organisms on earth, with an estimated 500,000 to 1,000,000 species. Only about 20,000 species have been described and the systematic literature is widely dispersed.

Soil nematodes: a large free-living stage of the insect parasite Psammomermis surrounded by smaller plant-parasites from the genus Helictylenchus.

Nematodes occur in all terrestrial, marine and aquatic habitats - from the bottom of the deepest ocean to near the tops of the highest mountains, from the tropics to polar regions and in every conceivable habitat.

They are found in or on most other types of organisms including earthworms, insects, molluscs, fish, reptiles, birds and mammals such as humans.

Nematodes can be:

  • parasites living off the body of their host
  • commensals sharing food with their host
  • phoretics using their host for transport.

Most nematodes are found in soil and eat microbes, other nematodes, microscopic animals or fungi.

Most are beneficial, greatly enhancing nutrient cycling and assisting in decomposition of organic wastes.

Nematodes are also useful in measuring the impacts of various perturbations on ecosystems, such as pollution, organic enrichment, and physical disturbance. Nematodes are intimately involved in many parts of the soil ecosystem, so they can be used as indicators of sustainability for soils.

Nematodes range in size from nearly 10 metres long to only a fraction of a millimetre (mm). However, they are mostly small, worm-like organisms, most of which are between 1 and 2 mm long.

A boat with 3 people in it approaching a hypothetical giant nematode in a river, the monster is shaped like a worm and is is rearing up.

Hypothetical giant nematode made up from all the nematodes in the Murray River

They vary in thickness from about 5 µm to 2.5 cm. If all the nematodes in the Murray River were combined into one huge animal, it would be over 20 metres long and laid end-to-end they would encircle the earth's equator.

All the nematodes on earth laid head to tail would reach the nearest star outside the solar system, Alpha-Centuri, over three light-years away, and back.

Although most nematodes are beneficial some nematodes attack the roots, stems, or leaves of plants.

Some transmit plant viruses and pathogenic fungi, while others cause galls on their host plants which impacts human economies in many ways; from loss of agricultural production, to pasture and turf damage, to invasion of forest trees, to adverse effects on the health of wild and domestic animals and humans.

Our Response

Understanding the implications to plant, soil and animal health

The team at CSIRO are actively working on a number of nematode projects, these include:

  • Curation & development of a national nematode collection: This project aims to develop and maintain collections of nematodes (associated with plants and invertebrates or free-living) in Australia.
  • Interactive illustrated identification keys to nematodes of Australia and ASEAN countries: This project is producing keys to all nematodes in Australia and ASEAN countries (particularly Laos, Thailand and Cambodia) at various taxonomic levels.
  • Training in Nematode identification and techniques: Bi-annual training courses are held in Australia and Asia for graduate students, technical staff, diagnosticians and advisors, run in conjunction with The University of Adelaide and the Thai Department of Agriculture.
  • Systematics of Australian Root-Lesion and Burrowing Nematodes: This project is describing and revising nematode species from the two economically important genera Aphelenchoides and Bursaphelenchus in Australia and Southeast Asia. They are of particular quarantine interest, and it is important to distinguish local species from exotics.
  • Classification of Phylum Nematoda to genus level: This project is integrating morphological, molecular and biological data to produce a comprehensive, consistent, cladistic classification of the entire Phylum, including over 25,000 species, 2500 genera and 300 families.
  • Movement of nematodes in trade networks: In collaboration with the Biosecurity Flagship, Plant Biosecurity CRC and Murdoch University, this project is determining which nematodes trade in agricultural produce in Australia and the region is transporting and how their movement can be managed.
  • Extraction methods: Ultrasonic waves are being used to extract nematodes from plant roots, particularly migratory plant parasites, in collaboration with the Thai Department of Agriculture.
  • Nematode Bio control: In collaboration with Charles Sturt University, we are using biological control agents to control nematodes of the genus Pratylenchus in grain crops.


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