Thank you to the lovely people who got in touch after reading my ‘slugg-ish’ column last week. Lots of you recommended nematodes as an organic and effective way to eradicate them. Although I have heard a lot about nematodes, I have never actually used them. Yet.
From the Greek ‘nematos’ (thread) and ‘eidos’ (species or form), nematodes are one of the most abundant creatures on Earth. They have adapted to colonise sea, fresh water, and soil and also to live as parasites inside plants, animals, and even humans.
Whereas most nematodes are perfectly harmless, and in some cases even beneficial to their environment or host, some are parasites. Unlike a predator, which is generally much larger than its prey and attacks from the outside, a parasite is much smaller and attacks from within. Parasites evolve to exploit a specific host, using that host’s resources for their own survival; often to the detriment of the host, causing weakness and sometimes death.
One nematode species – Phasmarhabditis hermaphrodita – has adapted to infest the body of many common garden slugs. It’s virtually impossible to detect by eye. Initially living on bacteria in the soil, the young nematodes seek out a slug host to continue their life cycle. Entering through the slug’s breathing hole (pneumostome) they take up residence, where the bacteria they ingested from the soil are released.
Within days, the ill-fated slug stops eating and retreats below ground to eventually die. The nematodes digest the decomposing remains, before producing a new generation that move off in search of new slug hosts.
Phasmarhabditis hermaphrodita are already present in the soil so you aren’t adding anything foreign to the garden. However, their natural numbers are insufficient to control the average garden’s voracious slug population, hence reinforcements are required. Once the slug population has diminished, the nematodes will die back to their natural levels again.
Thank you to Jayne for writing to tell me that she used them a few years ago on a garden in Monmouth and the slugs disappeared and never re-emerged, apart from the odd stray. And also that October is an ideal time to apply them as the eggs are being laid.
Thank you too, to Sarah who told me that a entomologist friend of hers told her that out of around 30 species of British garden slugs, only 13% do any damage. The problem is there is no way of telling which 13% it is!
And finally thank you to Chris for telling me that last year there was a knock at his front door and when he opened it he found a slug on the doorstep.
The slug said, I’m really thirsty, could I have a drink of water please?’
Chris picked the slug up and threw him over the nearest hedge.
Six months later there was another knock at the door. It was the very same slug. “What did you do that for?” he asked.
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