Have you ever wondered just how many nematodes there are in the world? These microscopic worms are the most abundant animals on Earth, making up nearly four out of every five creatures on the planet.
The surprising part is that most of them are harmless — and even helpful. Free-living nematodes enrich soil, recycle nutrients and support healthy crops. But not all nematodes are allies. Some can damage plants, infect humans and spread disease.
In this article, we’ll:
Most nematodes are considered free-living, meaning they function at several trophic levels of the soil food web and act as both prey and predator for other creatures. Free-living nematodes are some of nature’s most vital decomposers, recycling minerals and nutrients from bacteria, fungi and other substances back into the soil.
These unsung heroes contribute to soil health in several key ways. Nematodes:
Plant-parasitic nematodes don’t feed on bacteria, fungi and other microorganisms like free-living nematodes. Rather, they feed on plant roots by using their needle-like mouthparts, known as a stylet, to puncture plant cells and ingest plant fluids.
As you can imagine, this process isn’t ideal for plant health. Unable to obtain water and nutrients through their damaged roots, affected plants:
One of the most destructive plant parasites is the root-knot nematode. Unlike other nematodes that feed on plants from the outside, root-knot nematodes are ectoparasites that enter and feed from within roots.
This aptly named parasite injects hormones into plants that cause large, deformed galls (knots) to form throughout root systems. Below the ground, root-knot nematodes feed off of the enlarged roots, while above the ground, the plant wilts and possibly dies.
Plant-parasitic nematodes like the root-knot nematode cause an estimated $125 billion in global crop losses annually. However, the damage caused by nematodes that infect humans is far worse.
Intestinal nematodes are estimated to affect 3.5 billion people worldwide and cause approximately 125,000 deaths per year. They include:
Common symptoms of infection include diarrhea, abdominal pain and intestinal obstruction; however, nematode infections can result in far more serious conditions, such as anemia.
The majority of people infected with parasitic nematodes live in developing countries, where overcrowding, poor housing and a lack of sanitation lead to increased infection rates. Although intestinal nematodes thrive in tropical climates and developing countries, infections can also occur in developed countries like the United States.
Filarial nematodes are thread-like worms spread through insect bites that mature and mate in host tissues. Infection with these parasites can lead to two serious tropical diseases:
For better or worse, nematodes aren’t just in the soil; they’re sharing their planet with us. Understanding how they operate helps us appreciate how they, and other tiny organisms, impact the world around us.
Scientists are exploring new and effective ways to manage nematodes, from natural biological controls to studying how diseases spread.
Curious about these microscopic worms and how they’re helping (and harming) the way we live life on Earth? UF’s online entomology and nematology programs are a great place to start exploring this hidden world.
Sources:
https://www.apsnet.org/edcenter/disandpath/nematode/pdlessons/Pages/RootknotNematode.aspx
http://entnemdept.ufl.edu/creatures/nematode/soil_nematode.htm
https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/soils/health/biology/?cid=nrcs142p2_053866
https://edis.ifas.ufl.edu/ng005
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2517378
https://www.theatlantic.com/science/archive/2015/10/ivermectin-nobel-drugs-elephantiasis-filariasis-nematodes-wolbachia/409306
https://www.who.int/en/news-room/fact-sheets/detail/lymphatic-filariasis
https://www.cdc.gov/parasites/onchocerciasis/gen_info/faqs.html
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