Stigmella microtheriella

Wingspan 3 to 4 mm. The adults have purplish-bronzy wings with a silvery fascia, and darker purple outside the fascia. They closely resemble several other family members.  The larva mines the leaves of Hazel and Hornbeam, creating a very long narrow mine; in Hazel this often wanders all over the leaf; in Hornbeam it tends to be thicker and follow main veins.  The egg is underside, not in a leaf-axil. 

Stigmella floslactella

Adult Leafmine+egg positiion

Care is needed when trying to separate from those of Stigmella floslactella. The most reliable method of identification for this species is the egg position, S.floslactella lays an egg always on underside in a vein axil whereas S.microtheriella lays it often on or near a vein, but not in the axil. 

Areas where hazel is present.

They fly in May and again during August.

The larvae create narrow, often angular mines in the leaves of hazel and less commonly, hornbeam. Sometimes there can be several larvae mining the same leaf. The mines can be found in July and in October and November.

Widespread and fairly frequent in Britain. In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as common.

Occasional in Leicestershire and Rutland. L&R Moth Group status = C (very scarce resident or rare migrant).

http://www.leafmines.co.uk/html/Lepidoptera/S.microtheriella.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/monotrysia/nepticuloidea/nepticulidae/stigmella/stigmella-microtheriella/