Sialis is a genus of alderfly belonging to the order Megaloptera family Sialidae.

These alderflies are small and mainly brown with a relatively heavy body and forewings reaching a length of 10 to 20 millimeters.

The upper edge of the front wings consists of almost square cells.

The adults are diurnal and fly from May to June on the riparian vegetation.

Females lay on the leaves of the shore plants up to 2000 eggs in groups of about 200.