1a larva with well recognisable head; at least most of the mine full depth => 2

1b larva a maggot; mine essentially lower- or upper-surface => 4

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

2a larva without feet: Ceutorhynchus minutus

2b larva with thoracic feet, but without prolegs: Phyllotreta nemorum

2c larva with both thoracic feet and prolegs => 3

3a larva: pinacula white; older larvae live free under the leaf, producing little or no spinning: Plutella xylostella

3b pinacula black; older larvae live free (sometimes boring in the stem), producing much silk: Hellula undalis

4a frass powdery, in green clouds in remote corners of the mine: Scaptomyza flava

4b frass in black strings or pearl chains => 5

5a corridor pinnately branched, main and side branches on top of the midrib and lateral veins: Liriomyza strigata

5b corridor running through the leaf independently of the veins => 6

6a larva: rear spiraculum with 3 papillae: Liriomyza brassicae

6b rear spiraculum with 7-12 papillae: Liriomyza bryoniae