I share my garden with many different animals, but there is one which has more influence on the garden than any other; the worm. Whilst I am working hard above the ground, they are hard at work beneath. They complete the feedback loop of the cycle, converting the detritus of the year into compost and making its nutrients available to the plants again.
This week I had to do quite a bit of digging in the garden, filling in any gaps in the borders with late-summer flowering perennials. I was struck by the effect the worms were having on the garden. In areas where I found worms, the soil was much more friable, easier to dig, and the plants in these areas seemed to be thriving. In other areas the soil was hard, compacted, lacking organic matter and the plants were struggling to establish. Whilst the site of an earthworm is enough to send a young child recoiling in horror, I have come to regard them as my friends. When I spot them in the soil I know that we have a healthy soil, and the plants will thrive. Their absence provokes feelings of worry and doubt.
The action of earthworms burrowing improves the physical structure of the soil. They increase aeration, porosity and permeability, which means the soil can absorb more rainfall. They are one of the main organisms involved in the breakdown of leaf litter at the soil surface. They massively increase the surface area of the leaf litter allowing fungus to continue its breakdown, and enabling the release of valuable nutrients into the soil. Some deeper burrowing worms will even draw trace nutrients up from deep in the soil. A recent study found that compost created by earthworms (known as vermicompost) showed a huge increase in the germination and growth of many plants. Even adding just a small amount of the compost (5%) to multipurpose compost showed an increase in plant growth. Tests in the 1960’s demonstrated that crops grown in soils rich with earthworms showed huge increases in yields over crops grown in earthworm-free soil.
Earthworms are fascinating creatures. They do not have a skeleton, but much like a bouncy castle, are held up by the pressure of fluids inside their skin, which they also respire through. Earthworms are both male and female producing both eggs and sperm. The number of segments of each worm is consistent across the species, and individuals are born with the number of segments they will have throughout their life. Earthworms do not have eyes but instead have specialised photosensitive cells called ‘light cells of Hess’ ( I guess after the chap who discovered them?) The earthworm’s gut is a straight tube running from the head and mouth at one end to the anus at the other. Instead of being convoluted, like a mammalian digestive tract, it is folded internally to increase the surface area for absorption.
There are thought to be around 6000 species of earthworm worldwide and some earthworms in the tropics have been known to grow to almost 10 feet long. There are many types of earthworm that we can find in the UK, from the red ‘Brandling’ worms we often find in leaf litter or compost heaps to ‘Lob worms’, ‘Red-headed worms’ or the imaginatively named ‘Octagonal-tail worm’, each with its own preferred location and food source.
Earthworms habits fall into 3 categories. Those that live their life almost entirely in the leaf litter, like the Brandling. Those that burrow and recycle organic matter within the top 10-30cm of the soil, and those that construct permanent deep verticals burrows used to visit the surface and collect organic matter. One earth worm can digest up to 36 tons of soil every year, and there can be almost 8 million worms present in one hectare of healthy soil. The population of worms in the soil is dependent on availability of food, ph (worms prefer soils on the acidic side) and moisture content. Applying a regular coat of organic matter to the soil every year as a mulch will encourage a healthy population to develop and do the work of cultivating the soil on the gardeners behalf.
Earthworms are fundamental to many food chains. They are food for many birds such as crows, robins, starlings and thrushes (not just the early ones.) They are eaten by mammals like foxes, hedgehogs and moles, and even provide a food sources for insects, such as beetles. Earthworms are also sold as food for human consumption. Noke is a culinary term used by the Maori of New Zealand, and refers to earthworms which are considered delicacies for their chiefs.
In the 1960s the New Zealand flat worm was accidentally introduced to the UK, (probably hidden in a potted plant) and has rapidly settled into its new home. Whilst I am all in favour of increasing biodiversity, the New Zealand flatworm seems to have an opposing view, and has developed a disturbing taste for our earthworms. New Zealand Flatworms are usually found under pieces of wood, stone or polythene or lying curled-up on bare earth. They leave slime circles where they’ve been resting. The New Zealand Flatworms are flat, and look a bit like ribbons, with a dark purple-brown upper surface paler margins and a creamy, pale belly. They are usually about 0.3-1cm wide and 5-15 cm long, pointed at both ends and covered in sticky mucus. OPAL (open air laboratories network) are asking gardeners to keep an eye out for them and take part in a survey to find out more about their distribution by completing a short survey. You can find more information here: https://www.opalexplorenature.org/nzflatworm
In North America, earthworms were wiped out during the last Ice Age when a huge icecap extended south over much of the continent. As the ice retreated, the forests that sprung up were no longer dependant on the earth worm to provide its role as a composter. The organic matter built up quickly on the forest floor, and was utilised by other organisms instead. Earthworms were over the years accidentally introduced and began to chew their way through this bounty of food, radically altering the landscape around them.
In 1881 Charles Darwin wrote: “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.”
It is strange given how fundamental they are to our ecosystems in the UK, why we don’t consider them with more importance than we do. I know that without earthworms my garden would not be the same.