These minuscule, worm-like creatures that live in the soil can destroy pests, but they can also destroy crops.

Whether you’re a home gardener, a miniature farmer, or a commercial producer, soil matters. You can’t really tell robust soil from unhealthy soil by looking at it. But there are organisms in the soil—creatures you can’t see with the naked eye—that scientists utilize to measure soil health.

Nematodes are among the creatures scientists are looking for. These multicellular, worm-like animals are different from most other organisms in the soil, such as bacteria and fungi, which are single-celled. Roundworms have a digestive system. They are also crystal clear, making it easier for scientists to study their feeding habits.

Read more: Everything you need to know about the space-faring nematode: a worm like no other

I research nematodes that can be used as biological control agents and I also represent the University of Stellenbosch in South Africa in NEMEDUSSA Project. This is a consortium of 16 research and education institutes in Africa and Europe that work on and study nematodes. We want to escalate awareness, research and education about nematodes, especially in agricultural disciplines.

We also believe that it is crucial for everyone, especially for those working in agricultural sectorand even just casual food gardeners to know about nematodes. If you grow tomatoes in your garden, for example, root nematodes can cause complete crop failure.

There are four main types of nematodes in the soil. Each group has expert scientists who study their behavior and how they can be managed in agricultural practices to minimize the amount of damage they cause.

Free-living nematodes

Free-living nematodes are not parasites. They tend to feed on almost anything in the soil, including fungi, bacteria, and other nematodes. In fact, without these free-living nematodes, the soil is considered biologically dead and unhealthy for plant growth.

Plant parasitic nematodes

The uncontrolled accumulation of plant parasitic nematodes in unbalanced soil is a farmer’s nightmare. These nematodes feed through a needle-like stylet that they utilize as a syringe to draw food from plant roots. They have adapted their lifestyle from feeding outside the root to inside it, where they are protected from the harsh soil environment.

Plant parasitic nematodes can never be completely controlled. However, scientists have developed ways to prevent them from multiplying to harmful levels. These techniques include planting crops that are resistant to specific nematodes or rotating crops with crops that nematodes dislike.

Entomopathogenic nematodes

Entomopathogenic nematodes as biological control agents are my special interest. They are plant allies. They feed on insect pests, such as larvae and pupae, that come into contact with the soil, not the plants. Scientists recommend that every farmer or gardener have entomopathogenic nematodes in the soil, because they assist keep insect numbers low. Yes, you can buy them: they are available for saleincluding with some South African companies.

Parasitic nematodes of snails

Many snail species have close contact with the soil, which is why some nematodes have adapted their feeding habits to feed on snails over millions of years, and a few snails.

Scientists realized that the worm could be used as a biological control agent. Biocontrol involves using living organisms, such as pathogens or insects, to control pests, rather than using more environmentally harmful chemical products. A commercial product, available under the trade name Niemslug®, was developed in 1994 and exploits the feeding habits of snail nematodes for biological control. However, it is only available in Europe: research is ongoing to determine whether the species of nematode used in the commercial product occurs in South Africa and whether it is toxic to local endangered molluscs.

Monitor soil condition

My advice to gardeners and farmers, even small-scale farmers, is to send regular soil samples for laboratory testing. This will tell you what types of nematodes are living among your tomato plants – the “good guys” who take care of pests or plant parasites. There are many private companies (Few (is one example) in South Africa, which deals with this type of analysis and offers results-based consulting.