Leaf-miner: Circular, lower-surface blotch, about 5 mm in diameter, often quite a number together on a leaf. Upper surface wart-like, strongly reddish discoloured, opaque. At the lower surface the mine is closed only by the epidermis. The larva is easily visible, as is its food: drops of cell sap that oozes into the mine. Pupation sometimes in the mine, sometimes in the soil. (Bladmineerders van Europa).

The blotches are also illustrated in British Leafminers.

Larva: The larvae of flies are leg-less maggots without a head capsule (see examples). They never have thoracic or abdominal legs. They do not have chewing mouthparts, although they do have a characteristic cephalo-pharyngeal skeleton (see examples), usually visible internally through the body wall.

Initially white, later yellowish (Bladmineerders van Europa).

Puparium: The puparia of flies are formed within the hardened last larval skin or puparium and as a result sheaths enclosing head appendages, wings and legs are not visible externally (see examples).

Hosts in Great Britain and Ireland: Sonchus arvensis (Corn Sow-thistle), S. oleraceus (Smooth Sow-thistle), S.asper (Rough Sow-thistle)

Asteraceae
Sonchus	arvensis	Pernnial or Corn Sowthirstle		British leafminers
Sonchus	asper	Prickly Sowthistle		British leafminers
Sonchus	oleraceus	Rough Sowthistle		British leafminers

Hosts elsewhere:

Asteraceae
Sonchus	arvensis	Perennial or Corn Sowthistle		Bladmineerders van Europa
Sonchus	asper	Prickly Sowthistle		Bladmineerders van Europa
Sonchus	asper subsp. glaucescens			Bladmineerders van Europa
Sonchus	asper subsp. oleraceus			Bladmineerders van Europa
Sonchus	asper subsp. tenerrimus			Bladmineerders van Europa

Time of year - mines: Larvae from July on (Hering, 1957a); two or more generations per year, pupation of the summer generation(s) in the galls, pupation of the winter generation in the soil (Bayram, Skuhravá & Çobanoğlu (2005a) (Bladmineerders van Europa).

Time of year - adults: Currently unknown.

Distribution in Great Britain and Ireland: Widespread including Cambridgeshire, Durham, East Norfolk, East Suffolk, Fife, Glamorgan, Leicestershire, Pembrokeshire, Shropshire, South Lancashir, South-east Yorkshire, South-west Yorkshire, West Norfolk and West Suffolk (NBN Atlas).

Distribution elsewhere: Widespread in continental Europe including Austria, Belgium, Czech Republic, Denish mainland, Finland, French mainland, Germany, Hungary, Italian mainland, Lithuania, Poland, Romania, Spanish mainland, Sweden, Switerland, The Netherlands, Ukraine, and Yugoslavia (Fauna Europaea).

NBN Atlas links to known host species:

British and Irish Parasitoids in Britain and elsewhere: Currently unknown