Wingspan about 11 mm. The larva mines the leaves of Apple.

Adult Leafmine

Orchards, gardens and other places where apple trees are present.

Adults fly in May and June.

The young larvae mine the leaves of the foodplant, Apple (Malus), causing a gallery followed by a semi-translucent blotch on the upper surface of the leaf. It then vacates this and folds the edge of a leaf down to feed within, usually twice, before pupating externally among detritus.

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

It appears to be uncommon in Leicestershire and Rutland, where there are few records. L&R Moth Group status = D (rare or rarely recorded).

http://www.leafmines.co.uk/html/Lepidoptera/C.denticulella.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/ditrysia/gracillarioidea/gracillariidae/gracillariinae/callisto/callisto-denticulella/#:~:text=The%20mine%20begins%20as%20an,a%20characteristic%20orange%2Dbrown%20tinge.