29-Feb Leap Day Wonders

Before the creation of microscopes in the late seventeenth century no Londoner had ever seen or even imagined what could exist in a drop of pondwater. Hairybacks (Gastrotricha) are tiny, transparent flat creatures with blunt ‘whiskered’ heads and forked tails. Even professional microscopists miss them as they always hide, even when viewed down a microscope. Some are large enough that when swimming they can look like flecks of glass in the water. They are famous for “laying” eggs almost half the size of their body. Twenty different species occur in the ponds on Bookham Common including a contender for London’s rarest animal Chaetonotus ophiogaster intermedia.

Also in London ponds are an interesting group of flagellates. Gonium is one that exists as a free-living colony made up of just four cells. Pandorina is another, made up of just sixteen cells, Eudorina, thirty two and Volvox a few hundred. Many evolutionists believe this group shows closely the steps we ourselves may have taken as we evolved from a single-celled creature to a multicellular one many millions of years ago.

Parasites are another group with often hidden, complex and bizarre life cycles. Anyone who has seen parasitic fluke larvae (cercariae) leaving a host such as a watersnail is both amazed and appalled. For example, if a snail overheats, hundreds of worm-like cercariae simultaneously decide to abandon their host by just boring straight out of any part of its body wall.

Some parasitic water fleas look for all the world like miniature monsters. Anchistropus emarginatus is one with a fearsome sword-like beak the length of its body which it plunges into its victims, in this case hydras. They then indiscriminately rip their host apart using their legs to waft pieces of its flesh to their mouths.

Parasitic amoebas such as Hydramoeba hydroxena literally eat their hosts alive cell by cell till all that is left is a few hundred amoebas. Hairworms (Nematomorpha) are equally gruesome. It used to be thought they spontaneously generated themselves from hairs that fell out of a horse’s tail. We usually only ever notice them when we accidentally squash an insect and a worm almost the size of the insect itself is ejected from its body cavity.

February was a time when Londoners used to complain about fleas as they tend to get more active towards the end of winter. Their jumping ability is legendary with some being capable of jumping several hundred times an hour for several days looking for a new meal. It is said if one was the size of a man and stood on the steps of St. Paul’s Cathedral it would be able to leap straight over the dome.

On a lighter note, micromoths are another group hardly known to most of us. They are just tiny moths which because of their larger and more colourful relations just tend to get ignored. However, there are a thousand of them, mainly straw, beige or fawn in colour. We do notice those that eat our clothes as well as some of the more unusual such as the longhorns, plume moths, ermines and leaf miners. Others likely to catch our attention are the grass moths (Crambinae) which we often see running through the grass during summer picnics.

Stoneworts (Characeae) are yet another curious group. They look like delicate underwater horsetails but are in actual fact algae but so different they are in a class of their own. They tend to appear after ponds have been dredged but only as long as the water is crystal clear and unpolluted. They are usually coarse to touch due to an encrusting of lime. What is unique about them is that they can have individual cells up to five centimetres long which makes them the longest plant cells in the world. Several species turn up from time to time in London’s canals and ditches but Basingstoke Canal has long been the most reliable place to find them.

Nostoc is equally unusual. It is a cyanobacterium that is capable of creating blooms in lakes yet also lives on paths where it remains invisible until there is a shower of rain when suddenly the path is covered in small gelatinous balls. It is hardly surprising they were called witches jelly.

It would be quite easy to continue describing unusual creatures which are poorly worked upon and therefore relatively unknown, but before finishing water bears (Tardigrada) have to be mentioned. Their preferred habitat is the film of water that covers the surface of mosses.

Here they clamber about looking for all the world like miniature transparent bears with their eight legs ending in claws rather than the four you might expect. There can only be a handful of Londoners that could identify any of the thirteen species recorded on Bookham Common and the five recorded in Buckingham palace gardens. Various fascinating aspects of their biology are worth mentioning, not least their amazing ability to survive extreme conditions. They have been known to resuscitate themselves from one degree above absolute zero. At -272º C the molecular state of cells is substantially altered, yet within two hours they have been seen on the move again.

If they decide to form a cyst to avoid what they regard as adverse conditions they first moult but remain inside their cast skin. Then they slowly withdraw their “legs” back into their body and disassemble their organs into an amorphous mass of cells. When the good times return these cells then re-organise themselves into an entirely new water bear which then emerges from the cyst. Above all they are amongst the most comical of animals to observe. I have seen one fall through a drop of water, bounce on the microscope slide and then rear up on its “legs” a little like a grizzly bear and stare straight up the barrel of the microscope to what must have looked like a supernova, but was actually my eye.