What are Nematodes

Like me, you’ve no doubt heard of nematodes and how they’re touted as the miracle organic slug cure. But also, like me, you probably knew very little about them. So I’ve done some research for you and discovered that they’re quite fascinating little creatures.

To skip the facts and find out how to use nematodes against the slugs in your garden:

What is a nematode

Microscope image of a nematode

(Phasmarhabditis hermaphrodita)

From the Greek ‘nematos’ (thread) and ‘eidos’ (species or form), nematodes are one of the most abundant creatures on Earth; with a typical handful of soil containing thousands of the microscopic organisms. Over 20,000 different species have been classified, but estimates put the total at over a million!

Nematodes have adapted to colonise sea, fresh water, and soil; and also to live as parasites inside plants, animals, and even humans. They can be found from poles to tropics, from mountains to deserts, and in the depths of the oceans.

The slender multi-cellular worm-like creatures are typically less that 3mm (⅛") in length, although some can reach up to 5cm (2”). A few rare species are real whoppers; the largest ever recorded – discovered in the placenta of a sperm whale – was in excess of 8m!

Alongside nematodes, your garden soil plays host to a multitude of micro-organisms including algae, fungi, bacteria, and protozoa; all playing a fundamental role in the decomposition of organic matter into humus, and the recycling of vital nutrients that plants need to grow. It’s estimated that as many as a billion of these micro-organisms reside in a single gram of soil!

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.

How nematodes kill slugs

One nematode species – Phasmarhabditis hermaphrodita – has adapted to infest the body of many common garden slugs. At 0.5mm (0.02”) in length, 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.

Garden Slug infected by nematodes

Infected Garden Slug – note the swollen mantle

Nematodes tend to colonise the ‘mantle’ area; that saddle shaped region of the slug’s back that reminds us of its ancestry, the snail. This area becomes enlarged; a tell-tale sign that the creature is infected.

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.

Nematode production

Billions of slug infesting nematodes are bred in special facilities and kept in cold storage to keep them inactive. From there they’re shipped in special cool packaging to various approved suppliers, where they’re again kept refrigerated until ordered by you and I.

Nemaslug – nematode slug killer

Nemaslug pack

Nemaslug – Slug Killer

Nematodes are living organisms that need careful storage, which is why you don’t see them on the shelves at the garden centre. Instead, you need to order them direct from an approved supplier like Harrod Horticultural, who incidentally offer a good range of other garden products too.

Nemaslug is the brand you’ll find in the UK, and it’s available in two pack sizes:

  • Small Pack – Up to 40m² (50yd²)
  • Large Pack – Up to 100m² (125yd²)

The small Nemaslug pack contains around 12 million nematodes, the large around 30 million. Don’t ask me how they count them!

Nemaslug slug killer
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Nematode hosepipe feeder

Miracle-Gro nematode hosepipe feeder

Nematode hosepipe feeder

While a watering can is probably easiest and most accurate for treating a small area, a hosepipe feeder is ideal for larger gardens.

Manufactured by Miracle-Gro, this feeder is the one recommended for the hosepipe application of nematode products.

  • Three spay patterns.
  • Uses standard Hozelock fitting (supplied).
  • Suitable for foliar sprays and soluble feeds too, but wash thoroughly between different applications.

Nematode hosepipe feeder
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What do you want to do now

Organic Slug Killer

Nemaslug slug killer

The perfect choice for the ecological gardener who hates using chemicals and poisons in the garden.

Up to two months slug protection from a single application.

Harmless to birds, animals, and children. Safe to use on food crops. Dead slugs are non-toxic to other creatures.

Nemaslug slug killer
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Did you

Slugs used to live in the ocean, which is why they still need to keep moist

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