Willowfly Leuctra geniculata

 I found this little insect, about one centimetre long, on my car windscreen when I parked near Waskerley beck at Wolsingham in Weardale yesterday. I'm pretty sure its a willowfly Leuctra geniculata, a member of the family of needleflies within the order Plecoptera, the stoneflies. 

Needleflies' name comes from the way they tend to fold their wings tightly around their abdomen, making the insect appear slender and pointed.

It's a common insect but an encouraging sign of good water quality in the beck - stoneflies' aquatic larval stages need clean, well oxygenated water and have a low tolerance of pollutants.

Stonefly

I found this stonefly crawling on the footpath on Wylam bridge across the river Tyne yesterday.

Key identification features of stoneflies are their flattened profile, paired tail filaments and a strong propensity to scuttle along rather than fly.

Stoneflies, which are important food for fish and birds like dippers and wagtails. They're very sensitive to water pollution so their presence is a reassuring sign of good water quality in the river.

Click here for more on stoneflies.

Needlefly

I found this little needlefly which I think might be Leuctra hippopus [not too sure - this family of stoneflies (aka roll-winged stoneflies) has 13 genera with more than 300 species] on ramsons flowers beside the river Wear near Wolsingham a couple of days ago. It's one of the earliest of the stoneflies (Plecoptera) to hatch. This is a fast flowing, stony stretch of the river frequented by sea trout in autumn - stoneflies are good indicators of healthy, clean, well-oxygenated rivers. Characteristically, they fold their wings flat along their back and tend to be poor fliers, preferring to run rather than take to the air.

If the ID is wrong and anyone knows for sure what it should be I'd be glad to hear from them...

Tales from the Riverbank....

Many of the rocks along the banks of the upper reaches of the river Wear carry the empty nymphal cases of stoneflies, recognisable by the paired tail filaments. The split in the thoracic segments marks the point where the adult insect eased its way out of the nymphal exoskeleton after the nymph crawled out of the water.

Stoneflies tend to be confined to fast-flowing, well oxygenated, unpolluted rivers, which is a pretty good description of this stretch of the river Wear between Wolsingham and Black Banks, in Weardale. Currently, after a long spell without heavy rain, the water level is low and mayflies are laying eggs in the shallows and pools.

Mayflies are the only insects that moult in their adult stages. The winged adult that emerges from the nymph is the subimago (known to anglers as a 'dun') and this undergoes a final moult to become the imago ('spinner' in angling parlance). This is an imago that appears to be laying eggs, and drowning in the process. Females have shorter front legs than the males.

Mayfly nymphs have three tail filaments but the adults can have two or three tail filaments, depending on genus. The hind wings in mayflies are much shorter than the forewings....

.. and both pairs are held vertically above the body when at rest.

There are two large compound eyes and three small ocelli in between them. Adult mayflies do not feed during their short lives, so there are no functional mouthparts.

Male mayflies are notable for their extremely long front pair of legs, which are used to grasping females during mating flights.

During emergence and mating flights low over the water surface, vast numbers fall victim to fish - especially leaping trout - while those that survive fish predation ...

....become food for birds like dippers, which also feed on the nymphal stages of stoneflies and mayflies.