Radiographs of wheat infested by granary weevil, Sitophilus granarius (L.), were made daily from egg to emerged adult. Enlarged prints of the radiographs were mounted consecutively on illustration boards to facilitate study of development and habits of the weevils within kernels. Measurements of tunnel widths were used to determine instars. A series of 4 increases in tunnel width occurred, each of which was followed by 1 or more days of static tunnel width. Each period of increased width paralleled feeding activity; the static width formulated the following instar.