Alder fly

Alder Fly

Alder Fly ©

Alder fly

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Enw gwyddonol: Sialis lutaria
The Alder fly is a blackish invertebrate, with delicately veined wings that it folds over its body like a tent. It can be found near ponds and slow-flowing rivers; the larvae living in the silt at the bottom.

Top facts


Length: 1.4cm

Conservation status


Pryd i'w gweld

January to December


The Alder fly is a large, sluggish insect often found on vegetation near to water. The larvae are aquatic carnivores that live in the silt at the bottom of ponds and slow-flowing rivers. Adults are seen in early summer, emerging in large numbers and living for just for a few days in order to mate. Mating takes place at night and the females lay their eggs on overhanging vegetation. The larvae hatch and drop into the water where they develop over one to two years.

What to look for

Adult Alder flies are blackish-brown, with dark, lacy wings which they fold in a tent-like manner along the length of their body. They are distinguished from stoneflies by the lack of any 'tail' bristles.

Where to find


Roeddech chi yn gwybod?

The Alder fly is one of the most common aquatic invertebrates to be found in silty ponds.