Mine of the Month – May

This is the first 'Mine of the Month'. For details of the challenge see the previous introductory post.

This month's challenge is to find Eriocrania sangii, a leaf miner on birch. Here's the MMG species page. We currently only have one county record for this species (an adult seen at an MMG event at Hafren Forest) but it's likely to be under-recorded.

An adult Eriocrania sangii. Like most of this group, these are hard to identify
as adults (even by dissection) so it's much easier to record them as leaf mines.

We have six species of Eriocrania in the UK and all of these are found on birch (a point will be rewarded for finding any of these). Four of these species have been recorded in Montgomeryshire (but all six have been recorded in North Wales so there's the possibility of finding a new county record!).

Eriocranias make large blotch mines, which often take up much of the leaf (so are relatively easy to spot!). The larvae typically produce untidy, spaghetti-like frass. Here's a key for the birch Eriocranias. The first important feature is whether the mine begins at the edge of the leaf, or away from the leaf edge. You can work out the start point of the mine as the early mine is a narrow corridor (or 'gallery'), which later widens to form the large blotch. The early mine is often absorbed by the blotch but usually remains visible. In the photo below, the early corridor is visible running down along the leaf edge from the tip.

Eriocrania sangii mine. Image: Janet Graham

Two species start away from the leaf edge: E. salopiella and E. sparrmannella (however, the latter does not appear until later in the year). The remaining species all start at the leaf edge. If multiple larvae are within a single mine it's E. cicatricella. The remaining three species all have a single larva per mine: E.sangii, E. semipurpurella and E. unimaculella.

Eriocrania sangii is easily distinguished by its slate grey larva (all other Eriocrania larvae are white).

The distinctive grey larva of E. sangii. Image: Janet Graham.

A tip: smaller, seedling birches can often be more productive for leaf-mines, and different species can show preferences for different sized trees.

This is a somewhat difficult one for the first 'Mine of the Month' (others will be easier, I promise!) and this is why a point will be given to finding any one of the six Eriocrania species. At this time of the year, there's a fairly limited selection of active miners to pick from. Most leaf miners are summer-flying (so the mines appear a bit later in the year); however, the Eriocranias are typically on the wing in March and April, which is why the mines can be found from now.

Do get in touch if you want any help with ID.

Happy hunting!

Douglas

Update 07/05/20: With two new county records as a result of this challenge (E. unimaculella, Lake Vyrnwy, GBC and E. ciratricella, Middletown Hill, CBo), all six species have now been recorded in VC47!