The eggs of this species are laid on a leaf of creeping thistle or spear thistle (Cirsium vulgare), with the larvae mining the underside if the leaf, until a late instar where it feeds in a web under the midrib of the leaf, causing visible blotching on the upperside.
The larvae pupate in August, usually amongst the leaf litter, occasionally within the web.
The adults emerge in a single generation in September, and hibernate through the winter, re-emerging in spring. The moth often comes to light.
The species is found in England, Wales and southern Scotland.
Larva: (description Ian F. Smith)
Foodplant: July - early Aug. in brown leaf mine or silk tube under leaf of Cirsium vulgare and C. arvense. Continental Europe, reported on Arctium.
See also Cirsium key.
Length: 13 mm specimens in August described.
Head: Black with small translucent brownish patch subdorsally. Mandibles reddish brown.
Prothorax (T1): Anterior margin whitish. Prothoracic shield black divided by green median line.
Thoracic legs: Greenish yellow.
Body: Apple green or whitish apple green. Contractile dorsal vessel visible as indistinct darker dorsal line. Intersegmentally yellowish green.
Spiracles: Peritreme pitchy brown.
Pinacula: Concolorous with, but shinier than integument, slight greyish tint most marked on thorax.
Setae: Greyish brown, appearing greyish green in some lighting.
Anal plate: Concolorous with abdomen.
Prolegs: Concolorous with abdomen. Crochets reddish brown.
Similar species: Early instar larvae, under about 10 mm, of A. carduella are very similar. They lack the translucent subdorsal brownish patch on the head and usually occur in May and June, before propinquella.
The black pinacula distinguish late instar A. subpropinquella from A. propinquella and early instars of A. carduella. The writer does not know if early instar A. subpropinquella have black pinacula. If they do not, they could be confused with these two species. It is advisable to rear small larvae to over 10 mm, or to imago.