1a mine < 1 cm, full depth, often in numbers together in a leaf axil; larvae, with distinct feet and chitinised head, later live free and cause extensive window feeding: Epermenia chaerophyllella

1b mine > 1 cm, not full depth; larva a maggot => 2

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

2a large blotch with conspicuous primary and secondary feeding lines; larva: rear spiraculum with 3 papillae: Euleia heraclei

2b small blotch or corridor without apparent feeding lines; rear spiraculum with > 3 papillae => 3

3a frass in the lower-surface initial part of the mine sparse, often deliquescent; larva: rear spiraculum with 15-18 papillae: Phytomyza phellandrii

3b frass in this part of the mine as numerous black grains; rear spiraculum with > 30 papillae: Phytomyza oenanthica