The Eriocrania micro-moths are a relatively under-recorded group in the county as the diagnosis of the adults is not straightforward. There are eight species occurring in the UK and all of them have been found in Suffolk. The adults fly early in the year between March and May, the exact time depending on the species. The larvae feed by mining leaves and a recent key has meant that mines with larvae can be told apart. The mines can be found between April and June so now is a good time to go out and look for them.
The mines initially start off as a gallery before quickly becoming a blotch taking up a large area of the leaf. Sometimes the initial gallery remains visible in the blotch mine but in others may be lost. The dark frass occurs in loose thin coils within the mine.
The following is based on the Eriocraniidae key from the British Leafminers web site and my experiences with using it.
The first question to answer in working out the species is the foodplant
- Oak – see (1) Eriocrania subpurpurella
- Hornbeam or hazel – see (2) Eriocrania chrysolepidella
- Birch – see (3) Birch-feeding Eriocrania species
This is the only Eriocrania mining oak and is a very common and widespread species across the county and the adults often turn up at lights when oak trees are around. The mines are a frequent sight on oak trees. The figure below shows the typical leaf-mine and the white larva.
This is the only species mining hornbeam or hazel and is currently known from only one site in Suffolk, at Wolves Wood, where it has been found on both hornbeam and hazel. On hornbeam trees I found it easier to spot mines of this species by standing under the leaves with the sun shining through the leaves.
The six birch-feeding Eriocrania need a little closer looking at to distinguish them.
They fall into two groups so the first step is to decide which group
- The initial gallery mine starts on the leaf-edge but may be absorbed by the later blotch mine. This group of 4 species tend to mining earlier in the season than the second group. See (4) Leaf-edge birch-mining species.
- The initial gallery mine starts in the centre of the leaf, away from the leaf-edge. This group of 2 species tends to be mining in late May and June. See (11) Away from edge birch-mining species.
How many larvae are inside in the mine?
- More than one larva, usually two or three. Larva is pale white. See (5) Eriocrania cicatricella.
- Just one larva see (6) Single larva leaf-edge birch-mining species
This species appear to be scarcer than some of the other species but this may well be due to under-recording. Note the quite pale head of the larva.
What is the colour of the larva
- Grey – see (7) Eriocrania sangii
- Pale white – see (8) White single larva leaf-edge birch-mining species
The larva of this species is quite characteristic as it is grey in colour compared with the other Eriocrania species, which have whitish larvae.
There are now two species to split – Eriocrania semipurpurella and E. unimaculella.
Early instar E. semipurpurella larva can be easily spotted, often without taking them out of the mine as they have black head capsule and a large black spot just behind it. In later instars the head capsule becomes much lighter and the black spot appears to fade
For later instars the species can be split by answering the following
- Larva has a pale brown head. Lateral projections on 1st abdominal segment – sometimes I find these hard to distinguish. See (9) Eriocrania semipurpurella
- Larva has a darker brown head with dark spots at the posterior points of the head capsule. Lateral projections on 2nd abdominal segment – again I can find these hard to spot sometimes. See (10) Eriocrania unimaculella.
One of the larger species and also one of the commonest in the county. I don’t have any photos of the late instar larva at the moment but when I do I’ll update this section.
There are two species where the mine is started away from the leaf-edge – Eriocrania salopiella and E. sparrmannella. The mines and larvae can be found later in the year than the previous species and this helps distinguish them from those species that start mining from the leaf edge.
The two species can be separated based on the following features
- Mining starts in mid-May. Larval head is pale brown with darker mouth parts. There are dark transverse streaks posterior to the head capsule. There are lateral projections on the 1st abdominal segment. See (12) Eriocrania salopiella.
- Mining starts in mid-June. Larval head is brown with black lateral edges. There are two cloudy brown spots on the dorsal side of the prothorax. See (13) Eriocrania sparrmannella.
|E. salopiella head||E. sparrmannella head|
12. Eriocrania salopiella
13. Eriocrania sparrmannella