Alder Fly

Sialis lutaria


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.

How to identify

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 it


When to find it

  • January
  • February
  • March
  • April
  • May
  • June
  • July
  • August
  • September
  • October
  • November
  • December

How can people help

The Wildlife Trusts manage many wetland nature reserves for the benefit of all kinds of wildlife, from bugs to dragonflies, fish to Otters. But these precious sites are under threat from development, drainage and climate change. You can help by supporting your local Trust and becoming a member; you'll find out about exciting wildlife happenings, events on your doorstep and volunteering opportunities, and be helping local wildlife along the way.

Species information

Common name
Alder Fly
Latin name
Sialis lutaria
Other insects
Length: 1.4cm
Conservation status