black spruce borer

Black spruce borer, also called opaque sawyer, is a common, widespread, small to medium-sized, longhorn beetle. It is considered holarctic, native both in the Palearctic realm (Europe and Asia) and in the Nearctic realm (North America). It occurs throughout most of the United States and southern Canada, but it is absent from the Great Plains, the Great Basin, and the Desert Southwest.

Adults are active during the day from April through July in coniferous and mixed forests. They are found on various conifers, especially pines but also spruces, firs, Douglas firs, and tamaracks. Adults are found mostly at the bases of stumps, on recently fallen trees, and on lower trunks of weakened or dying trees that have been damaged by wind or fire. The larvae bore oval tunnels up to 5⁄16″ (8 mm) wide, at first under the bark but later in the wood. Adults create slightly flattened, almost round exit holes when they emerge.

Adults are 5⁄16″ to 1″ (8 to 25 mm) in length. The body is robust, dark, and dull. It is usually black, sometimes black to brown or dark brown, occasionally light brown. The surface is densely covered with short, fine hairs.

The head is short and wide. It is not narrowed behind the eyes. The eyes are shallowly notched around the bases of the antennae. The antennae are less than half as long as the body. That is medium length for a beetle but short for a longhorn beetle. They have 11 segments. The second segment is about equal to or slightly shorter than the ninth. On the male, the fifth segment is longer than the third. On the female, the fifth and third segments are the same length.

The plate on the first segment of the thorax (pronotum) is evenly rounded on the sides when viewed from above. The lateral margins are not flattened.

The wing covers (elytra) have 2 to 4 parallel ridges. This is the feature that gives the beetle its species epithet.

The legs are usually dark, sometimes light. The last part of each leg (tarsus), corresponding to the foot, has five segments, but the fourth segment is minute, and it is concealed between the lobes of the heart-shaped third segment, making it appear that there are only four segments.

Total length: 5⁄16″ to 1″ (8 to 25 mm)

Coniferous and mixed forests. Pine, spruce, fir, and tamarack.

April through July

Sources disagree about when adults are active. One author reports that they are active during the day (diurnal), one that it is active at night (nocturnal), and one that is is active at dusk and dawn and at night (crepuscular/nocturnal). All sources agree that they will come to lights at night.

Females deposit clusters of several eggs each into crevices in thick bark.

Sources

24, 27, 29, 30, 82, 83.

Asemum striatum
Ophrus

Asemum striatum
Will_wildlife

20200814 Asemum striatum
Nicolas Tavernier

Luciearl
5/4/2025

Location: Lake Shore, MN