We studied the biology of Scolytus subscaber LeConte (Coleoptera: Curculionidae: Scolytinae) in grand fir, Abies grandis (Douglas) Lindley, in northern Idaho. Presented are new Idaho distribution records, description of the mature larva and adult, biological features, characteristics of infestation and galleries, and natural control factors. The beetle has one generation per year, taking flight in July to infest live branches in the crowns of mature trees. The uniquely shaped egg gallery deeply scores the wood; its two arms curve inward like the Greek letter ε. Eggs are laid along the outer edge of the gallery; hatched larvae mine hidden in the phloem for a short distance after which they mine next to the sapwood where they overwinter. A cerambycid, Tetropium abietis Fall, occurred often in the larger diameter portion of branches infested with S. subscaber. A scolytid, Scolytus abietis Blackman, also infested branches but not those containing S. subscaber. Mortality factors included a braconid parasitoid, Ecphylus arcuatus Muesebeck, on larvae and the flooding of egg galleries with resin evidently caused by defensive response of the host tree to a staining fungus, Spicaria anomala (Corda) Harz., carried by the beetle. In addition, we point out errors and lack of documentation concerning the identity, biology, and behavior of S. subscaber in secondary published sources.