Alderfly Larvae

Sialis lutaria

Statistics

Taxonomic family: Sialidae

Length: 1 to 2.5 cm

Average life span: 1 to 2 years

Juvenile stage (in water): 1 to 2 years

Adult stage (out of water): less than 2 weeks

When To See

The larvae are around all the time. The pupas are based on riverbanks. While the adults tend to hatch April to late June.

Photo credit: Iain Reid, commons.wikimedia.org & Jim Rathert (Missouri Dept. of Conservation)

Habitat

Larvae tend to like ponds and lakes, hanging out in areas of silt and slow flow. In rivers they like slow flowing pools and in larger rivers (such as the lower sections of rivers), but they can also be found in fast flowing streams where there is still plenty of silt for them to dig about in. The adults are generally poor flyers so are never found far from the waters edge. As the adults don’t eat (living off reserves they built up as a larvae), while the larvae are carnivorous, preying on smaller animals they find on the bottom of the river.

How To Identify

Adults are blackish-brown with dark, lacy wings. Front wings fold like a tent along the whole length of the body. Similar to stoneflies but with a lack of tail setae (bristles).

Seen It?

Been kicking about in your local river and come across one of these invertebrates? Not sure? Share it with us at trust@forthriverstrust.org, we enjoy chatting about inverts with you.

Larvae stage