The small square-spot (Diarsia rubi) is a moth of the family Noctuidae.

This is a quite a small species (wingspan 30–38 mm) with dull greyish-pink forewings, varying to red brown, marked with a pale angular mark which gives the species its common name.

Forewing with the crosslines and shades olive; the cell brown; reniform with whitish outline; claviform with a dark speck at its end; marginal area dark.

The hindwings are pale luteous grey with a pink fringe.

[1] Two broods are produced each year with the adults flying in May and June and again in August and September.