Dark Sword-grass Agrotis ipsilon
Wingspan 35-50 mm.
One of Britain's most regular migrants, it can appear in large numbers in some years, and then be relatively scarce in others.
Occurring in any month between March and November, it is however most numerous between August and October, and though more frequent in the south, can turn up almost anywhere.
The larvae feed on or below the ground and at night, on various herbaceous plants and their roots. Due to its retiring nature, breeding in this country has never been reliably proven.