The Cabbage Webworm or Old World Webworm (Hellula undalis) is a moth of the Crambidae family. It is a widespread species which is found from Europe across Asia to the Pacific. It was first described from Italy.
The wingspan is about 18 mm. Adult moths have fawn forewings, each with sinuous pale lines and a kidney-shaped mark. The hindwings are a uniform grey darkening at the margins.
The larvae feed on a wide range of plants, mainly of the Brassicaceae family. Recorded foodplants include broccoli, crucifers, head cabbage, Chinese cabbage, spoon cabbage, daikon radish, horseradish, mustard, radish and turnip. It is considered a serious agricultural pest. The larvae initially bore into the stem of growing shoots, later instars mine the leaves and leaf stems. It makes a web of silk around the feeding area which accumulates frass. The caterpillar is 12–15 mm long and is whitish with pinkish-brown longitudinal stripes.
Pupation occurs within this silken shelter. The pupa is formed in a loose cocoon of webbed-together particles of soil or other matter and is about 8 mm long, shining pale brown with a dark stripe on the back.