Saturday, 4 April 2009

Water bugs

There are some water bugs that are familiar to just about anyone who has ever been pond-dipping. Included among these are the pond skaters and water boatman that make use of the surface tension to eek out a living. However, there are all sorts of other weird and wonderful invertebrates that can be found in our ponds, rivers and streams; some can even be found in cattle troughs. All you need is a net, a white plastic tray in which to sort through your haul and a decent hand lens. Armed with such kit you should be able to turn up something of interest in all but the coldest weather. Even now, so early in the year there is plenty to be found.

Late winter or early spring is actually quite a good time to go looking for corixid bugs, some of which look quite similar to the more familiar water boatman, though they typically swim the other way up. As a group they can be regarded as being highly successful, with representatives found from Iceland to New Zealand and from ice-bound pools to hot springs and even the saline waters of estuaries. They are mainly herbivorous and feed on algae collected from the bottom of weedy ponds, slow river backwaters and dykes.

One of the most commonly encountered species around here is a bug called Corixa punctata, which also goes by the rather unimaginative English name of the Common Corixid. The first adults of the year emerge in mid-July and overwinter in the adult form. Mating takes place in January or February and soon after this the males die, leaving the females to lay their eggs over the few remaining weeks that they have left. The eggs are laid in small batches, each batch being attached to the stem or leaf of an aquatic plant. As the females approach the end of their all too brief lives, so the number of eggs laid diminishes, the females using up the resources they have left.

If you ever go to the trouble of catching or keeping Corixa punctata you’ll soon discover two interesting things about it. First, like many other water bugs it is endowed with a pair of stink glands from which the bug can release a noxious substance to deter would-be predators; the smell is really rather unpleasant. The other interesting feature is that these small creatures communicate by stridulating, making a characteristic ‘zip-zip-zip’ sound that can be heard over several metres. They do this by rubbing a special patch of short hairs on their front leg against a resonant part of the head. Having them do this in an aquarium can be rather unnerving, as you cannot easily tell where the noise is coming from.

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