Key for the identification of the known mines of British
insects (Diptera and non-Diptera) recorded on Polypodium

1a > Leaf-miner: Large full depth blotch, covering the entire distal part of a pinnula. The mine begins near the top, where an elliptic egg shell is attached to the underside of the rachis. Larva solitary. The mine contains much frass.

An upperside blotch at the tip of a pinna lobe.

On Pteridium and Dryopteris, but not yet on Polypodium, in Britain. On additional other genera of ferns elsewhere. Widespread in Britain and continental Europe. Also recorded in East Palaearctic and Near East.

Chirosia histricina Rondani, 1866 [Diptera: Anthomyiidae].

1b > Leaf-miner: Larva forming short linear mine in single section of a frond. Pupation external (Spencer, 1972b: 58).

Large, very transparant blotch, with primary and secondary feeding lines. In the centre a concentration of black frass. Mines can coalesce, and then contain several larvae. At the start of the mine, at the leaf underside, a white egg shell. However, the larva can leave its mine and restart elsewehere, therefore mines without an egg shell may occur as well.

A small marginal upper surface gallery in a single section of frond.

On Pteridium aquilinum and Polypodium vulgare in Britain. Also Asplenium elsewhere. Widespread in Britain. Also recorded in the Republic of Ireland. Widespread throughout Europe.

Phytoliriomyza hilarella (Zetterstedt, 1848) [Diptera: Agromyzidae].

1c > Leaf-miner: Larva forms a long greenish linear mine, frequently following a vein; mines can be up to 10 cm long. Pupation internal; anterior spiracles projecting through the leaf epidermis (Spencer, 1972b).

Corridor, with the frass in an almost uninterrupted line along one side. In small leaves the corridor often follows the margin, but when space is not limited, like in Hart's-tongue Fern, it curves smoothly, not infrequently running over the midrib for some distance. Pupation mostly within the mine; the anterior spiracles then penetrate the epidermis.

Forms a long narrow mine (up to 10cms). It is normally greenish and upper surface.

On Asplenium ruta-muraria, Ceterach, Phyllitis scolopendrium and Polypodium vulgare in Britain and in addition to these Asplenium scolopendrium and Asplenium septentrionale and Ceterach officinarum elsewhere. Widespread in Britain. Also recorded in the Republic of Ireland. Widespread in much of Europe.

Chromatomyia scolopendri (Robineau-Desvoidy, 1851) [Diptera: Agromyzidae].