The larva of Bucculatrix cristatella feeds on Yarrow in a leaf mine to begin with, then later feeding externally on the leaves, shrivelling and blanching or browning them. Twice during its growth, it spins a white cocoonet in which it moults its skin. The cocoonet is constructed on the upper surface of a leaf, where it is easily detected. If held up to the light, the larva, or its cast skin retaining the larval shape, can be seen. Like other Bucculatriginae, the pupa, on the foodplant or adjacent plants, is in a distinctive whitish ribbed cocoon.