The moth's evolution has been affected by the industrial melanism that occurred in Europe during the late 19th and early 20th centuries, causing a dramatic increase in two aberrations (salicin and lugubris), which have darker grey wings.

However, as it is part of a UK Priority Biodiversity Action Plan and receiving greater awareness and conservation, the species may become more abundant.

[1] A white spot is seen midway down the trailing edge of the forewing providing a distinct marker for A. rumicis not seen in other Acronicta moths.

Forewing dark grey, varied in places with whitish; lines and shades black; outer line marked by a white spot on the submedian fold; hindwings brownish fuscous Larva marbled dark and light grey: a dorsal row of red spots on black blotches, and a row of white spots on each side; a pale line below spiracles, containing orange-red tubercles; segments 5 and 12 of dorsum humped; tubercles with fascicles of fuscous and fulvous hairs— turanica Stgr., a form from Central Asia, is much paler, with the hindwings whitish.

— Chinese and Japanese examples (3k) are larger than European and in all cases darker; in particular the lower half of forewing is blacker and the white spot of outer line then often obscured; possibly the scotch form figured by Curtis as salicis, a melanic form, may represent this aberration, though the larva figured as belonging thereto is unquestionably that of menyanthidis.

is pale yellowish grey with numerous black lines and the orbicular stigma faint or obsolete, occurring in Cornwall.

Noctuids are commonly known as "owlet moths" because of their large eyes that shine in the dark and the colour of their wings which make them difficult to see.

[5] According to Thomas Algernon Chapman, the genus Acronicta can be split into three major groups: The first, characterized by a hoop-like structure of the pupa and clumped oviposition, includes: A. auricoma, A. myricae, A. menthanthidis, A. venosa, and A. rumicis.

The second, characterized by terminal spines of pupa and dome-shaped ova laid apart from others, includes: A. psi, A. tridens, A. strigosa, A. alni, A. megacephala, A. leporina, A. aceris.

[7] At the caterpillar stage, A. rumicis tends to feed on low-growing, herbaceous plants, including sorrel, dock, bramble, thistles, hop,[8] and occasionally on the leaves of shrubs.

The eggs have a round flattened shape like a sand dollar and has a micropylar area that has 20 long ridges that radiate from the center, almost like a child's drawing of a sun and its rays.

Although the general cause of trouble in the life of A. rumicis is parasitism via parasitoids, another group of predators includes small birds.

The aberration salicis Curtis, which is commonly found throughout the moth's distribution range, has darker grey-blotched sections on wings and retains the A. rumicis identifying marker, the white spot on its forewings.

The aberration lugubris Schultz is almost completely black, lacking the mixed-grey mottling on the wings, but still retains the prominent white spot marker on its forewings.

[16] With the industrial period in the past and resting surfaces less darkened by soot, it is reasonable to see that evolutionarily, the melanic variations are no longer as favourable.

In A. rumicis, duration of light and temperature are two major factors causing diapause, the slowing or stopping of development in an insect when environmental conditions are not optimal.

When A. rumicis were exposed to light on a short day, or 6–15 hours in the experiment, during the larval feeding period, almost all individuals underwent diapause after reaching pupal stage.

[17] As the daily photoperiods extended past 17 hours, the incidence of diapause began to drop, not causing any change to the development of the pupae in the cocoon.

[19] According to a study in Poland, A. rumicis has also taken over maize populations, feeding until the leaves of the corn plants are no longer fresh and new because of the shift into harvesting season.

During the spring and summer, the larvae of these moths damages both the leaves and silks of the cobs, occasionally eating soft kernels as well.

Recently, A. rumicis was assigned as a Priority Biodiversity Action Plan (BAP) species, meaning the moth was identified as most threatened and will immediately be part of conservation efforts.

[21] According to Emma Coulthard, hedgerows in close proximity to crop plants and farmlands are highly important to the survival of moths like A. rumicis.