I HAVE always held a fascination for invertebrates. They exist in our world and we can to some extent interact with them but we have to really work our imaginations if we are to hope to get a glimpse of what their world is like.

Invertebrates, with perhaps a few exceptions like the giant squid, live in a world that is separated from ours by scale. What to us is a smooth lawn would appear to them as a hostile impenetrable jungle.

To cross the lawn by foot might take us 30 seconds but to them it would be a treacherous journey. However, the thing that is uppermost in my mind, is that I am very glad I will never have to live in their world, at their scale, as life in small scale always looks hideously terrifying and inhabited with monstrosities.

Finding invertebrates in December is a little tricky but there are always a few spots, like under logs that will never let you down. Sweep a tray or a net through the waters of a pool in late spring and you end up with a writhing mass of life to look at but in December, there is a lot less but it is still there.

Return that life to the pool and odds-on clinging to the tray or net you will find a flatworm.

Initially these are easily missed as they contract themselves up and look more or less like a small blob of dark coloured jelly. Wait a moment and they will pick up their courage and extend to small sensory horns and begin to glide along extremely smoothly.

Get out the magnifying glass and you find out what a bizarre world they live in.

Flatworms, are one of the simplest organisms to be blessed with a brain or more correctly two. Scientists have tested flatworms and found they are able to learn simple tasks. Their brain is fed by sensory information by two rather simple eyes, which are not able to form images but help the flatworm differentiate from light and dark. It has an acute ability to taste its surroundings and by analysing these chemical traces it is able to explore its environment and hunt for food.

British freshwater flatworms are mainly predatory, targeting any thing small enough for it to catch. Flatworms are very different to true worms have no segments and don't have the ability to wriggle. They are, as their name suggests, flat and this is due to their lack of a respiratory system which makes them dependent on absorbing oxygen directly from their surroundings and being thin means once absorbed this oxygen has not far to travel.

Watching the flatworms sedately glide around, propelled by thousand of microscopic beating hairs and sliding on a thin layer of slime, one starts to wonder how such a slow, apparently defenceless animal could ever be a predator. Well its secret is in the slime. Try wash one off and its takes quite the effort as this slim is sticky and it leaves a little behind as it travels, just like a slug and any unfortunate small animal who comes across it is likely to be come stuck, easy pickings for the slowly approaching flatworm.

Reproduction in the flatworm family in the summer months is very similar to true worm relatives but in the winter the flatworm will often deliberately stick the tip of its posterior end to a suitable immovable object and begin to tug away with its front end until it literally tears its self apart. Then unlike true worms who only mythically have the powers of regeneration, each part of the flatworm begins to regenerate whatever organs that segment had lost as part of the separation. Even if a flatworm is forcibly and involuntarily ripped apart each separated segment will begin the process of regeneration to create more individual flatworms. This power of regeneration matched with the poisonous nature of its sticky slim make flatworms extremely difficult to kill. This has led to flatworms becoming highly successful animals, that inhabit almost every imaginable body of water. I am just glad that the physiological constraints of this successful body design have prevent it from growing to any great size or these flatworms could prove to be a fearsome adversary.

11:40am Monday 10th December 2007

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