Agonopterix assimilella is a moth

Moth

A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

 of the Oecophoridae

Oecophoridae

Oecophoridae is a family of small moths in the superfamily Gelechioidea. The phylogeny and systematics of gelechoid moths are still not fully resolved, and the circumscription of the Oecophoridae is strongly affected by this....

 family. It is found in most of Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

.
The wingspan

Wingspan

The wingspan of an airplane or a bird, is the distance from one wingtip to the other wingtip. For example, the Boeing 777 has a wingspan of about ; and a Wandering Albatross caught in 1965 had a wingspan of , the official record for a living bird.The term wingspan, more technically extent, is...

 is 15-21 mm. Adults are on wing from April to June.

The larvae feed on Cytisus scoparius

Cytisus scoparius

Cytisus scoparius, the Common Broom and Scotch Broom, syn. Sarothamnus scoparius, is a perennial leguminous shrub native to western and central Europe,....

. They initially feed inside the stems, but later feed externally between two green stems sewn together in parallel. Larvae can be found from October to February. The species overwinters in the larval stage within the stem.