In a nematode's shoes

Year of Soils column by Wim van der Putten

And so I find myself cycling in the rain, trying to imagine what it’s like to be a nematode. Nematodes or roundworms are tiny animals – typically less than one-tenth of a millimetre long and one-hundredth of a millimeter thick – that live in a thin film of water around grains of sand in the soil. They move like professional swimmers, wriggling their bodies underwater as they turn. Not much like me on my bike at all, then. Although at least I, too, am surrounded by water.

Not all nematodes have the same diet. Some eat bacteria, which they pick off grains of sand with antler-like protuberances - like stag horns, only really tiny. Other nematodes feast on fungi or plants. They have a hollow stinger - a stylet - that they thrust forward to suck liquid from plant cells…a bit like sipping lemonade with a straw. Finally there are nematodes that feed on other nematodes. These have a sharp tooth or spear that helps them snaffle their prey. I must say just thinking about all that feeding and feasting on my bike makes me feel peckish. But I’m still a long way from home.

So…why was it again that I started doing research into nematodes? Well, without them nature would be quite boring. There would only be one or two species of plants, covering everything. Nematodes help to maintain diversity. But how exactly they and other soil organisms manage to do that, remains largely a mystery.

Farmers aren’t quite so fond of nematodes when their crops are afflicted by them. ‘Potato sickness’ for instance, isn’t some kind of virus as you might expect but just a fancy way of saying there are too many potato cyst nematodes in the soil, causing growth retardation. Yet nematodes can also control plant pests such as slugs and snails: as the saying goes, one man’s poison is another man’s meat. Oops…here I go thinking about food again!