A total of 14 known fatty acids and one unknown fatty acid were detected in the third instar, fourth instar, prepupa, and female and male pupae of the eastern hemlock looper, Lambdina fiscellaria fiscellaria. The C8:0,3 C10:0, C22:1, and C24:0 fatty acids and an unknown fatty acid were not detected in the third instar larvae, and the unknown was also absent from the fourth instar larvae. The C24:0 fatty acid was absent from the prepupae and both the male and female pupae. The C22:1 fatty acid was absent from the prepupae. Otherwise, developmental stages contained the C8:0, C10:0, C14:0, C15:0, C16:0, C18:0, C18:1, C18:2, C18:3,C20:0, C20:1, C22:0, C22:1, and the C24:0 fatty acids and the unknown fatty acid. In general, the level of a given fatty acid decreased with succeeding developmental stages. The lipid level was also determined for each developmental stage.