Worrying about worms

There can’t be many gardeners who aren’t pleased to see a worm in their soil. We know instinctively how important these little creatures are, even if we haven’t visited Down House in N. Kent where Darwin conducted 40years of worm experiments.

In Darwin’s own words "there are few animals which have played so important a part in the history of the world than the earthworm", by creating and maintaining the health and structure of the soil.

So this year, with that in mind, I started to worry about what was happening to the worms in my garden, particularly when the drought really kicked in with the hosepipe ban. How would they survive in bone-dry, hard soil? Thanks to Google I got some answers.

When soils get dry, earthworms go into estivation. This is where earthworms wrap their bodies into a tight knot to reduce the amount of surface area exposed to the soil. Then they seal themselves in a chamber lined with mucus where the humidity stays high so they don’t dry out as the soil dries. Experiments show that they can survive in estivation for 3 weeks. Another tactic they can use is to burrow deeper into the soil to find dampness, some can go as deep as 6 feet apparently.

If the worst comes to the worst and individual worms die, there is still the survival of eggs which are encased in a cocoon. The amount of time that they take to hatch can vary by species, but also by the weather with some able to wait out undesirable drought conditions within the soil at the cocoon stage.

Of course there hasn’t just been drought this year, we have had floods too. For years scientists thought the reason earthworms came to the soil surface after a downpour was to prevent drowning in their water-filled burrows. However, we now know that earthworms breathe through their skins and actually require moisture in the soil . They are unable to drown like a human would, and they can even survive several days fully submerged in water.

Needing moisture to survive, soil experts now think earthworms surface during rain storms for migration purposes, giving them the opportunity to travel more easily across the soil surface than they could underground.

Then there has been the recent snow and frost! Once again they have their survival tactics. 10cm under the ground the soil is often a few degrees warmer than the air and many soil animals are still active, including earthworms. When temperatures fall below 0°C and water in the soil freezes many earthworms simply burrow into deeper layers where they can survive. Also they can avoid freezing by increasing the amount of sugars in their body fluids, this reduces the temperature at which they will freeze, a bit like putting antifreeze in a car. Finally earthworm cocoons are very resistant to cold. The cocoons of the common surface-feeding earthworm Dendrodrilus rubidus is known to survive temperatures below −40°C and in the laboratory have survived immersion in liquid nitrogen at −196°C!

So, all in all, our ultimate ‘Garden Friend’ is pretty resilient. But what can we do to help? Well, the good news is that our moisture-retentive Kentish clay soil is very good for earthworms and if we add organic matter, such as well-rotted manure, compost or leaf-mould the worms will love it. Shrubs and hedges and their resultant covering of decaying leaf litter also help, as well as providing shelter under their thermal mass in the same way that a decaying log pile will benefit worms and a multitude of beneficial creatures. Avoiding digging as much as possible will let the worms do the work for you, but if you must dig use a fork, as there less chance of slicing into a worm than digging with a spade. Finally, natural surfaces encourage living soils, so if you have areas of paving or other artificial surfaces you can use the techniques above to create areas rich in worms in other parts of your garden. A win win situation for all.

More information:
The Earthworm Society of Britain
Earthworm Watch