posted in: Invertebrates, Warwickshire | 0

As with last Friday’s sawfly, here’s something called a fly that isn’t actually a fly at all, having two pairs of wings. Once again, the clue is in the name of the taxonomic order: Diptera have two wings, and Megaloptera have big wings – though ‘big’, obviously, is a highly relative term. The wings are impressively obvious though, as are those of other members of the order, such as dobsonflies and fishflies, which are well-known in the USA but which we don’t have here in the UK. At one point they were listed as part of the order Neuroptera, or net-wings, but now that belongs to insects like the lacewings and snakeflies, and the megalopterans are out on their own – which is fair enough, I think, because you’d hardly describe these wings as delicate. To me they look more like frosted and leaded windows, and if my assessment of what was being eaten here was correct, they’re very chewy indeed.

There are three species of alderfly in the UK, but I’ve used the name Sialis lutaria for this creature because it’s much the commonest, and therefore the likeliest to be seen (the only way to tell them apart for sure is to examine their genitalia, and frankly I didn’t care that much). Sialis lutaria is sometimes called the mud alderfly because its larvae develop in silty environments at the bottom of ponds and rivers, where they predate other small aquatic creatures. Larval development takes up to two years, after which the larvae emerge onto land and pupate. The adults live no more than a few weeks, during which time their only aim is to complete their life cycle by breeding. Females lay large clumps of eggs on vegetation overhanging appropriate water – there’s a good photo of that here – and as soon as they hatch the larvae drop into the water to start the cycle again.

The reason I was excited enough about this rather drab insect when I spotted it on the bank of the River Avon today to squat down in a nettlebed to photograph it, was the realisation that it’s the first insect I’ve seen this year that has unquestionably emerged from water, to complete its life cycle on land and in the air. Thus it marks the beginning of my season of haunting river banks and ponds, in search of Odonata. The Avon isn’t likely to produce any of those yet – I don’t believe I’ve ever found any damsels or dragons along its banks before May – but I know that Large Red damselflies are already emerging in warmer parts of the country, so shallower water bodies are worth checking from now on.