A ‘big’ fish in a small pond

I WAS cleaning up my pond the other day.

The pond is small, and when the sun comes out in July the water warms up rapidly. This often leads to an increase in the growth of algae, which can choke the oxygenating plants that keep the water sweet.

I was lifting these plants, gently pulling off the algae and replanting them. I noticed movement in the algae, which I was about to throw away.

Closer inspection revealed a number of creatures, of varying size, from very small to about a centimetre long, which all looked rather like wood-lice.

The resemblance isn’t a coincidence, because these aquatic crustaceans are close relations of the terrestrial wood louse. They have a number of English names, but the commonest is the rather unflattering ‘water hoglouse’.

There are two similar species and they are common in shallow water that is still or slow-moving. However, it is a mystery as to how they arrived in my pond, which is filled with treated mains water and a long way from any other hoglouse habitat. Unlike many of the aquatic insects that have colonised the pond, these crustaceans do not have a flying phase in their life-cycle. The pond is also too small to attract water birds, which often carry small aquatic organisms from one water body to another.

Anyway, I caught as many of the hoglice as I could and carefully returned them to the pond. This was not only because I was concerned for their welfare, it was also because I was aware of the good work they were doing in there.

As far as I know, there is no aesthetically pleasing way of stopping dead leaves from blowing into your pond.

If enough leaves blow in and start to rot, the water will soon become foul and stagnant. My pond is small enough for me to pick out the leaves — but spending hours on my knees, with my hands in the water, is not my favourite job.

Luckily, dead leaves are the favourite food of the water hog-louse. And, as a bonus, their second favourite food is the algae I was trying to get rid of. Definitely a useful animal.

Nature Table

THE ELDER TREE (Sambucus nigra)

Elders have been in flower for a couple of weeks now, their froth of creamy white blossom dominating many hedgerows and filling them with a heady, sweet scent.

Soon these flowers will turn into bunches of berries, first green, then red, finally ripening to black. Elder is a native tree, capable of reaching 10m in height with a single trunk covered in deeply fissured bark.

However, it’s often damaged by wind or hedge-cutting machinery and reduced to a shrub. It’s not a popular plant in Ireland, and over most of Europe has been associated with bad luck. This is unfortunate because the flowers are an important source of nectar for insects and the berries provide food for many birds and small mammals and humans who use them in drinks, jams and chutneys. The seasoned timber is hard and dense and much better for firewood and other uses than most of the experts admit.


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