Hand-lens descriptions of extruded dry frass are given for 5 wood-boring insects that attack living black, scarlet, and red oaks, namely, the red oak borer, Enaphalodes rufulus (Haldeman) and the living-beech borer, Goes pulverulentus (Haldeman) [Coleoptera: Cerambycidae]; a clear-winged moth, Paranthrene palmii (Hy. Edwards) [Lepidoptera: Aegeriidae]; and the carpenterworm, Prionoxystus robiniae (Peck), and the little carpenterworm, P. macmurtrei (Guerin-Meneville) [Lepidoptera: Cossidae]. The 2 constituents of frass—excrement pellets and wood pieces—are described according to their shape, length, color, and solidity. Knowledge of the frass characteristics of these insects helps in identifying the boring species and in revealing the stage of larval development, molting periods, and mortality. Further, knowledge of the length of wood slivers and/or pellets of excrement generally produced by the insect permits prediction of adult emergence.