Pond-dipping

Pond-dipping with children is hardly a scientific affair but it is great for raising their interest and understanding of the natural world.

The usual haul at this time of year includes dragonfly nymphs and ferocious looking diving beetle larvae but tadpoles and sticklebacks are the children's favourites.

Once the children have finished I usually wave them goodbye and then set about giving the nets and collection trays a rinse.

Inevitably some life still clings to these trays with a surprising determination and what strange creatures these are.

Gliding across these trays in a way which looks almost magical, are small, 1cm long flatworms.

Flatworms are fascinating as they are, for me, creatures that push the limits of how strange life on earth can be.

Scaled up a bit, flatworms would make excellent monsters for an episode of Dr Who, Star Trek, or even the X Files.

There are many different species of flatworms, or turbellaria as they are more correctlyl called, and some of these can be quite strange, even for flatworms.

Most have an obvious head and many have two prominent eyes, but here the familiarity to most animals' body patterns ends.

The flatworm does not keep its mouth on its head but has it centrally mounted on its belly.

Many flatworms are predatory and hunt quite actively by either propelling themselves through the water by beating millions of tiny hair-like cilia or more commonly by gliding along on a film of slime like a snail or slug.

This slime is the flatworm's weapon, at it is highly poisonous and it uses this to subdue and trap its victims.

The victim is then hauled into the flatworm's mouth for digestion in its strange, many-branched gut which is often visible through its almost transparent body.

The slime is also an excellent defence as it is poisonous enough to deter most predators.

Flatworms lay eggs, like many invertebrates, but they can just split in half to produce two new worms.

Like any horrible fictional monster, flatworms are hard to kill and even if broken into quite tiny pieces, each piece will continue to live and regenerate into another flatworm.

Unlike many other invertebrates, they can also thrive in cold conditions. Species can be found in near-freezing waters, in mountain streams and deep underground, in caverns and caves.

Described like this, they would seem to be unstoppable creatures, able to take over the world and, in fact they have, and have done so for hundreds of millions of years.

However, most are small and have no impact on humans, so go mostly unnoticed.

They also have an Achilles heel which prevents them growing and becoming predators, which we certainly would take notice of. They have no active means of breathing or a circulation system, and this prevents them from growing.