Upwardly mobile snails

One of the stranger sights of autumn is the way in which snails seem to have a compulsion to climb to the top of hogweed Heracleum sphondylium stems during wet weather. These are just a few of over 50 that I counted on a single hogweed plant recently.

They seem to have a passion for the thin layer of soft rotting tissues on the outside of the dying plant's stem.

Snail trail art

Feeding trail left by the abrasive radula (tongue) of a garden snail inside a plastic bucket in our garden. The bucket had been filled with rainwater and developed a lining of slimy algae, which dried on the surface when the water was tipped out - then the snail moved in.

The Snail, the Woodlouse and the Millipede with disgusting but valuable habits...

If this post title sounds like a modern-day Aesop's fable well, in a way it is, because it does have a moral. Not one, but two morals...

Have you ever wondered what millipedes eat? Probably not, but if you have the books will tell you that they are herbivores that sometimes eat gardeners' seedlings and are therefore a pest.

When I found this millipede clinging to the back of a garden snail's shell I wondered what it was up to. Could it be that millipedes attack snails? If so, they'd go up in my estimation.

All was revealed when the snail glided away, almost running over a woodlouse in the process but leaving some tell-tail evidence: snail poo.

Yes, remember you read it here first: millipedes eat snail poo. 

Maybe not the most pleasant addition to the sum total of human knowledge, but there is a moral to the story. 

Millipedes do indeed eat some of the gardener's seedlings but they are also part of a vast community of soil invertebrates that play a role in cycling of minerals. This snail poo might well be all that's left of some lettuce seedlings I planted out a few days ago, but at least I'm secure in the knowledge that, once they've passed through a millipede's digestive system, some of the nutrients will find their way back to the soil and feed the next batch of my seedlings that a snail snacks on....

The second moral is that the only sane way to approach vegetable gardening is to recognise that you are part of the great web of food interactions and nutrient recycling, and to become reconciled to the fact that some of what you plant - sometimes most of what you plant - is going to pass through the digestive system of a snail and maybe a millipede too, rather than your own.

So, I think of gardening as a source of endless photo-opportunities and don't expect to harvest too much. It's the way to reach gardening karma. 

So, on to the next question: if you are a snail, what does it sound like when a millipede walks past? Probably, like this...

Wildlife on Walls: 4. Garden Snail, Helix aspersa

The recent hot, dry spell has triggered some distinctive behaviour in snails that helps these moisture-loving molluscs survive long, dry periods.

It's called aestivation and involves the animal secreting a thick layer of mucus that cements the mouth of the shell to a hard substrate, minimising water loss. 

The shady side of an old stone wall with plenty of gaps between the rocks is the perfect place to aestivate through a drought and numerous snails often pack themselves into these crevices, until the classic British wet summer returns. Like many invertebrates, the internal organs of dormant snails shrink substantially once they've sealed themselves in their shell and stop feeding.

The Benefits of being Hermaphrodite

It's seed-sowing time again - a time of hope and expectation, tempered only by the knowledge that the garden snail population is waking up too, ready to chew its way through all that tender new growth. Some time ago I devised a way of reducing the garden snail population by giving them somewhere to spend the winter where they could easily be found (click here) and then transported into the countryside. These two, caught in the act of mating, are a couple that I missed.


Garden snails Helix aspersa are hermaphrodite but nevertheless exchange sperm, as these two are doing. Being hermaphrodite is one of the secrets of their success because it means that every individual in the population can lay eggs and produce offspring; if animals exist as separate genders, either male or female, only half the population can lay eggs.


Click here to see some images of snail eggs and click here to see the baby snails that emerged from them.

Snail in a Hurry

A few days ago Ron Bloomquist published at interesting photo of a ‘hiccuping’ intermittent snail trail on his Walking Fort Bragg blog, and was wondering how it might have come about (see http://walkingfortbragg.com/2009/07/so-how-foggy-was-it.html) .This snail wandered across my path today and this series of photos shows quite nicely how hit moves, with a head-to-tail wave of muscular contraction along its foot which is slightly arched – check out the way the gap under its foot moves backwards as the snail moves forwards in this top-to-bottom sequence (double-click the images for a larger, clearer view). It occurs to me that if the snail was crawling along a hot road surface and wanted to minimise the exposure of its foot to the heat it might well arch its foot even more, and might leave a trail like the one Ron saw...........just a thought.