Everybody who keeps fish knows that they are often fed on water fleas. They are so small that their life history is not well known.

This is a pity because when seen under a microscope there are actually a number of very similar species, and it takes a real expert to work out the differences.

The wonder of the Daphnia is that the internal structure can be seen through the transparent shell — including the food canal, through which the passage of microscopic plants which the animal has eaten can be studied. Also visible are the eggs in the brood chamber, and even the beating of the heart.

The large compound eye, made up of many parts, and the muscles controlling each of them, is equally fascinating. The Daphnia keeps its place in the water by vigorous strokes, and a pair of antennae which propel it in a series of jerksm and hence its common name suggesting the motion of a flea.

Daphnia and the flea, however, are not related in any way.

Even though you need a microscope to see the details I have described here, the flea- like movements can be seen just by doing a pond dip anywhere in Britain.

They are the most common creature found in our waters, and are crustaceans.

Looking out for frog spawn

The first few days of January followed the wet miserable trend so typical of 2012, but this is the time of the year when it is just possible to look out for the first signs of spring.

I’m always interested to find the first frog spawn — last year it was February 10, and sleet was falling, and a chilly wind was blowing.

In recent years, more interesting facts have emerged relating to the life history of the frog. There were reports concerning tadpoles being found in early March.

It seems, however, that some tadpoles which develop slowly in cold summers are able to hibernate in the winter. They then complete the life cycle the following spring when the weather warms up a bit. Another aspect of the frog’s life history is that they seem to have traditional breeding ponds.

Young frogs emerging from their “birth ponds” move away, but seem to remember the area and return there to breed.

When animals go through several different stages during their life cycle as is the case with frogs, toads, butterflies and many other insects, it is referred to as metamorphosis.

This comes from the Greek and translates as many stages. which is a good description.

Plant is a sign of Old England

Like many people I always salute the first snowdrop of the year, but for those who watch carefully there are other flowers which bloom early.

On January 3, I spotted my first primrose, which I admit did look very sorry for itself, but it had at least made an effort to beat winter.

Also on this day I found the first signs of dog’s mercury.

Why dogs? The old Anglo-Saxon word for dog meant common, so that is ok. Why mercury? This was because the plant was boiled up and used to treat bowel disorders. Mercury was also given to patients with digestive problems, despite the fact that we now know that the liquid metal is poisonous.

These old fashioned “cures” did much more harm than good. No doubt patients felt better if they had been sick!

To modern-day botanists, dog’s mercury is known as an indicator species. Its ancient habitat was in the old native woodlands.

Wherever the plant grows in numbers suggests that the area was once an area of woodland. Because both its leaves and flowers are green means that dog’s mercury is overlooked. The point is therefore missed that here is an indication of Old England.