MEGALOPTERA > Sialidae

 

Although not closely related, Alderflies are often studied together with Lacewings, Scorpionflies and Snakeflies in a combined group known as the NEUROPTERIDA (click 'allies' link for further information).

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Their common name tends to imply that they have a close association with Alders, but that's not so, as Alderflies are just as likely to be seen on any tree that is alongside or overhangs water. However, from my limited encounters so far, they're best observed amongst bankside reeds where they're easier to see and photograph.

 

Only three species of Alderfly occur in Britain; all very similar in appearance and indistinguishable from photos alone. One though, Sialis nigripes, is nationally scarce with no official records of being seen locally, so realistically I'm only likely to come across either of the two common forms, which fortunately are habitat specific. Whereas Sialis lutaria may be found along the margins of some slow-flowing rivers, it is essentially a wetland species that's predominantly at home on ponds and lakes. Sialis fulginosa, on the other hand, is a flowing water species that, in theory, would not be encountered at a still water location such as Longham Lakes or Crane Lake at Moors Valley CP.

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Adults have broad flattened heads with biting mouthparts, and two pairs of soft, heavily veined, similar sized, wings that completely hide the abdomen when the insect is resting. The head and exposed pronotum are black, and the wing veins dark brown or black. Once seen and recognised, they are pretty much unmistakable. 

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