The forewings of the silver-Y moth (Autographa gamma) have varied markings, from different shades of brown to grey, but the most distinctive feature is the irregular white mark. The hindwings are brown with a broad, dark band along the margin. The body is light brown and hairy, the antennae are long and thin. The moths fly during the day as well as at night, often in large swarms. They fly rapidly from flower to flower, often resting with their wings folded roof-like above the body.
The female lays up to 2,000 eggs on the underside of the leaves of their host plant, usually separately but sometimes in small groups. These eggs are a greyish white, suffused with a blue-grey in the middle and they have irregular surface ridging. The caterpillars have a small head that is grey-green to brownish green, sometimes with a black lateral line. The body has stiff hairs and is usually greenish with a light lateral line. Below the lateral line there is a dark dot on each segment. Dorsally there are alternating light and dark stripes. A characteristic feature of this caterpillar is the oscillatory swaying movement of the anterior end. The caterpillars are nocturnal. When the caterpillar is full-grown, it will form a greenish to black pupa, either in leaves which are woven together with silk threads, or in a suitable hiding place spun somewhere in greenhouse material.