Leaf-mine: Flat green corridors in the leaves. The only character to separate this species from Hydrellia griseola is that adult flies of griseola are dusted greyish-white, those of thoracica not dusted, greyish brown (Hering, 1957) - see also Bladmineerders van Europa.

Larva: Details unknown.

Puparium: Details unknown.

Comments: Irwin & Chandler in Chandler (1978) did not indicate whether their host record was British or Foreign and is therefore included under 'Hosts in Britain' and 'Hosts elsewhere', as is the record by Pitkin and Plant, which was previously assumed to be British.

Hosts in Britain:

Hosts elsewhere:

Time of year - mines: April (Hering, 1957).

Time of year - adults: Unknown.

Distribution in Great Britain and Ireland: Recorded in Britain by Irwin (1978); Cambridgeshire, Dorset, East Kent, Glamorgan, Middlesex, Monmouthshire, North Somerset, South Wiltshire, Surrey, West Lancaster, West Suffolk and Westmorland (NBN Gateway - N.B. includes Watsonian Vice Counties having publicly available records that fall within or overlap the vice county border at 10km resolution or better i.e. a record for a vice county may relate to an adjacent vice county - for included datasets see NBN Grid map below).

Also recorded in the Republic of Ireland (Zatwarnicki, 2004 in Fauna Europaea).

NBN Grid map: Note that not all datasets on the NBN Gateway may be available on the map below. If you are an NBN Gateway registered user you can request access for missing datasets via the link 'Open interactive map in new window' below.

Distribution elsewhere: North and Central Europe including The Netherlands (Bladmineerders van Europa), Belgium (Gosseries, 1991d), Austria, Bulgaria, Czech Republic, Finland, French mainland, Germany, Hungary, Italian mainland, Poland, Romania, Slovakia, Sweden, Switzerland and The Netherlands (Zatwarnicki, 2004 in Fauna Europaea).

NBN interactive distribution map(s) of known host species in Great Britain and Ireland and elsewhere:

Parasitoids in Britain and elsewhere: Unknown.