When I first recorded this leaf mine (found on 24 November at Cosmeston Lakes Country Park, where there is rather a lot of it in one particular area), it was named ‘Record of the Week’ by SEWBReC, the local biodiversity records centre, and hailed as only the third Welsh record (though the national recorder for this species later corrected this, as it seems several records from north Wales had not been added to the Welsh database at that stage). Since then, I’ve found these mines in five more locations, proving that once again this is an under-recorded leaf-mining species.
These leaf mines were made on Stinking iris (Iris foetidissima) by the fly Cerodontha iridis, and they can also be found in Britain on other Iris species, though I haven’t seen any of those. The mines occur in early autumn, though they can still be seen on Iris leaves later than that – I’m seeing them now, in early winter. Often the adult fly lays several eggs on one leaf and, after the larvae hatch and start munching, they create blotch mines, which may be quite large when several mines coalesce.
You can read more detailed information about this species and see some excellent images, including close-ups of the larvae and their puparia, on the Bladmineerders website here.