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Eriocraniidae: leaf mines and larvae of the birch feeding species
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There are six birch-feeding Eriocraniidae (Lepidoptera) on the British checklist. The larvae all feed in blotch-mines which contain long inter-twining threads of black frass. The larvae develop rapidly, feeding being completed in about a week. The larval markings change several times, probably at each instar. The full-grown larvae leave the mines, and are believed to remain in the ground until the following Spring before pupating.

 In two species the mines begin well away from the leaf-edge, and these can be separated by the different timings of larval feeding.

In the other four species the mines begin from an egg-site at or close to the leaf-edge. The egg is presumably laid before the leaf is fully developed, as there is often a small hole or distortion of the leaf-tissue at the start of the mine. The edge of the leaf is often torn at this point. The mine may start with a short length (5 to 10mm) of narrow gallery with linear frass before widening abruptly to a blotch. These features are sometimes absorbed in the later part of the blotch, and not visible. These four species all have larvae feeding during May, and the very similar mines can only be separated by identifying the larvae.

Where larvae have lateral projections on abdominal segments, these are often difficult to detect when the larvae are in the mines.

1
The mine begins well away from the leaf-edge, with a narrow gallery containing linear frass. This feature is normally still visible when absorbed in the later blotch 2
 
The mine begins at or near the leaf-edge. A short length of linear feeding, if present, widens abruptly to a blotch 3
2
The early gallery, in the centre of the leaf, is absorbed by an elongate-oval blotch. This leads to a large blotch on the leaf-edge. Larval feeding begins in mid May. The final-instar larva is white, with pale brown head and darker mouth-parts. Lateral projections on first abdominal segment. This mine is the penultimate Eriocrania mine to appear (Eriocrania sparrmannella being the last). It is one or two weeks later than the other birch feeders. Eriocrania salopiella
 
The early gallery, in the centre of the leaf, is somewhat angular and absorbed by a narrow angular blotch. This leads to a larger blotch on the leaf-edge. Larval feeding begins in mid June. The final-instar larva is white, the head brown with black lateral edges. On the prothorax (dorsal surface) there are two cloudy brown spots   Eriocrania sparrmannella
3
The blotch, on the leaf-edge, contains more than one, usually two or three, pale watery-white larvae     Eriocrania cicatricella
 
The blotch contains only a single larva 4
4
Larva dark grey Eriocrania sangii
 
Larva whitish 5
5
Larva (final-instar) with pale brown head. The largest and commonest species. Lateral projections on first abdominal segment Eriocrania semipurpurella
 
Larva (final-instar) with darker brown head. The posterior points of the head-capsule show as two large black spots. Lateral projections on second abdominal segment Heringocrania unimaculella

 

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