I AM fascinated by the way garden ponds are colonised by wild aquatic plants and animals.
Even if you only use sterile tap water to fill them and only introduce living things from a pet shop or garden centre, unexpected underwater wildlife soon appears.
The two ponds I built this year are very small and very new but it’s already starting to happen. I suspect it would be happening on an even greater scale if I didn’t have fish in the lower pond. A true wildlife pond is probably better off without them because they tend to eat the smaller creatures and even nibble on the plants – but it’s hard to resist the temptation of goldfish.
A friend of mine has a larger and more mature pond and he emailed the other day, rather excited because his son had discovered water scorpions (above) in it. It is a strange and rather fascinating creature.
They’re insects (true scorpions, of course, are crustaceans) and belong to the Order Hemiptera, which are usually known as bugs. The bugs include insects such as cicadas, aphids, leafhoppers and shield bugs, amongst others. Most of them live on land, boring holes in plants with a sort of beak at the front of their head and sucking sap with it.
But water scorpions are different. The’re fierce predators, large bugs, growing to a bit over two centimetres in length. Their flat oval body is brown so that they can spend time lurking in water plants pretending to be a dead leaf. On the front of this body is a pair of fierce looking pincers and on the back what looks like a long, whip-like tail.
In fact it’s a snorkel. Water scorpions are air-breathing and they use this device so that they can spend long periods of time below the surface waiting to ambush their prey without running out of air. They literally breathe through their rear ends.
The pincers do look a bit like those on a scorpion, or maybe a Dublin Bay prawn, and are used to catch prey. This mostly consists of smaller water insects, though they can manage small tadpoles and even fish fry.
The mystery of how water scorpions got into my friend’s pond is easy to solve. Like most insects, they can fly. They don’t do this very often, possibly because it spoils their fierce and macho image – the wings are diaphanous and a rather effeminate shade of pink.
Pond skaters are also bugs and they have evolved an unusual strategy for colonising garden ponds. In any community of pond skaters most of the insects have no wings, or only very rudimentary ones, and are incapable of flight. But in every community there are a few individuals with fully formed wings, so they always have the opportunity to utilise any new habitat that may appear.
But plants can’t fly –neither can things like water snails, freshwater shrimps and the water louse, which is an underwater version of the wood louse. How do they get into ponds? The most likely answer actually sounds rather unlikely. They probably came down in the last shower. Seeds, eggs and tiny larvae can be sucked up when water evaporates, survive a journey into the clouds and descend again into your pond. There are even authentic records of it raining small frogs.
If you find something interesting in your pond and you want to know what it is I recommend, go to the website of the Irish Peatland Conservation Council which has something called a Bogwatch Pool Bug Dial which is an excellent tool for identifying pond life. See: www.ipcc.ie/bicbugdial.pdf
* dick.warner@examiner.ie
a d v e r t i s e m e n t
This appeared in the printed version of the Irish Examiner Monday, August 10, 2009
