Adults average 4 mm in length and are among the largest species of native Scolytus . Males have a well defined tubercle on the second abdominal segment. Females have a faint tubercle or none at all. Scolytus adults are characterised by a ventral posterior concavity. Outbreaks occur following periods of tree stress due to drought, disease and defoliation.
Breeding also occurs in slash and windthrow trees.
Living trees may be killed outright by the attack, top-killed or may survive repeated attack. Egg galleries are distinct because they are scored deeply in the wood and cut transversely across the grain of the wood from each side of a central entrance chamber. Occasionally Douglas-fir , Tsuga and Picea . It kills an estimated 450 million fbm in California annually.