These moths mainly inhabit deciduous forests, hedgerows, parks and gardens, at an elevation up to 1,600 metres (5,200 ft) above sea level.

(The Latin specific name also refers to these markings, as resembling the Greek letter psi, ψ.

The moth is very similar to the dark dagger (Acronicta tridens) and identification is generally only possible by minute examination of the genitalia.

The larva of Acronicta psi is quite hairy, greyish or brownish below and black above, with red spots along the sides and a bold yellow stripe along the back.

The grey dagger flies at night from June to August[a][3] and is attracted to light and sometimes to sugar.