1a corridor long and narrow, sometimes ending below the water line; older larva lives free in a case: Nymphula nitidulata

1b corridor broader, irregular, never ending submerged; older larva lives as a stem borer => 2

1c galls, etc => Tables for all parasites per species

2a larva: anal shield with a thickened rim, ending in two diverging teeth: Orthotelia sparganella

2b anal shield flat, untoothed: Globia sparganii