Key for the identification of the known mines of British
insects recorded on Geranium

1a > Leaf-miner: An initially narrow linear mine which after the first moult widens into large linear or irregular blotch; frass in distinct rows in the early linear section, later more scattered (Spencer, 1976: 128-9, fig. 221).

The mine is described by Hering (1957a) as follows: Upper-surface mine. The start is corridor-like and generally follows the leaf margin. Further on the mine widens considerably, forms a secondary blotch and gets irregular sides that are deeply eaten out. Primary and secondary feeding lines clearly visible. Frass mostly in large clumps. Pupation outside the mine. The mine only rarely occurs in Geranium robertianum; the frass then is fine-grained and the mines are smaller. Hering didn't think it impossible the the miners of Geranium robertianum and the other Geranium species might be a different species. Dutch material might form a different third species.

The first instar larva makes an initial corridor, with frass in two lines. Then a large irregular blotch is formed.

On Geranium in Britain and Geranium and Erodium elsewhere. Widespread in Britain and continental Europe.

Agromyza nigrescens Hendel, 1920 [Diptera: Agromyzidae].

1b > Leaf-miner: A long gallery with dispersed frass. Oviposition may be at either side of the leaf, not necessarily close to a vein. The mine is a not very tortuous corridor, not widened in the end. Frass in a broad central line. The mine strongly overlaps with the one of S. splendidissimella.

On Agrimonia, Fragaria, Geum, Potentilla and Rubus, but not yet on Geranium, in Britain plus Geranium elsewhere. Widespread in Britain and continental Europe.

Stigmella aurella (Fabricius, 1775) [Lepidoptera: Nepticulidae].

1c > Leaf-miner: Rather narrow corridor, untidy and sometimes branched, starting from the base of the leaf, in particular the midrib. Sides of the corridor irregularly eaten out, not really parallel. Frass mostly present, and then in a central line. The larva is capable of leaving the mine and start a new one elsewhere. These later mines are much broader, and the frass is scattered irregularly..

Host plants unknown in Britain. On numerous genera and species in several plant families, including Geranium, elsewhere. Recorded in southern England. Widespread in continental Europe.

Orthochaetes insignis (Aube, 1863) [Coleoptera: Curculionidae].