It is the end of May and, along the Derwent outside my door, the Stoneflies are beginning to appear. These are pretty ancient insects (Order: PLECOPTERA) who've been around for the best part of 300 million years or so, about 50 million years or so before the True Flies (Order: DIPTERA) appeared on the scene. This one was just about to scuttle into that wood joint, so the picture was a bit rushed. Let me show you another, also taken on the banks of the Derwent, to show you how to recognise them.
|Yellow Sally, Isoperla grammatica|
This one is called the Yellow Sally and, starting at the head end, she has a pair of long, segmented antennae. She also appears to have two at the back, but rear projections from insects are called cerci. In most insects, both antennae and cerci are sensory organs but they're far more sensitive than the front and rear sensors on your car. Look at the wings next. They are either held flat over their backs, or slightly rolled around their abdomens (which helps to tell them apart from Mayflies which also have two cerci). The vein structure of the stonefly wing is quite complex and the name of the order, Plecoptera, comes from the ancient Greek for braided wings.
Females will lay up to a thousand sticky eggs which will adhere to rocks in the river for two or three weeks before hatching into nymphs. These will live in the river for up to four years before emerging as adults. Like many insects, the adult life is quite short; just a few weeks. You can find them anywhere in the world except Antarctica, provided the water is clean (they are a good indicator of water purity). They are herbivorous, although some species do not eat at all as adults, and quite harmless to us humans. Anglers like to use the nymphs for fly fishing and I have read that the nymphs are edible, although I haven't been able to verify that fact, so don't try them at home.
Here are a couple of books on stoneflies, one for naturalists and one for anglers, but if you don't fancy shelling out that much on one order of insects, all the major stonefly facts are covered on pages 44,45 and 78 of The Quick Guide To Creepy-Crawlies.
All the best,
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