Home / Longhorn Beetles (Cerambycidae) / White-spotted Sawyer (Monochamus scutellatus)

White-spotted Sawyer (Monochamus scutellatus)

White-spotted sawyer beetle of the longhorn beetle family is a wood-boring species indigenous to different parts of North America. The white spots on the wings of both males and females earn them their name.

White-spotted Sawyer Beetle

Scientific Classification

  • Family: Cerambycidae
  • Genus: Monochamus
  • Scientific name: Monochamus scutellatus

Physical Description and Identification

Adult

Size: 20 – 25 mm (0.78 – 0.98 inches)

Color: They have a metallic black body, withwhite spots near the base of their elytra.

Other Characteristic Features: The antennae in males are twice the length of their body, while it is comparatively shorter in females. In both the sexes, a spine is seen to the side of their prothorax.

White Spotted Sawyer

Larva

Their body and head are creamy-white and reddish-brown. A full-grown larva reaches 40 – 50 mm (1.57 -1.96 inches), burrowing in the cambium and phloem upon hatching, remaining there till they pupate.

White-spotted Sawyer Larvae

Pupa

The pupae reach a length of 20 – 25 mm (0.78 – 0.98 inches), initially pale white, later turning to reddish-brown. Their legs, mouthparts, wings, and antennae are incomplete then. The appendages, too, are less prominent, eventually developing as they mature. Upon complete development, the pupae harden and become darker.  The pupation stage lasts for a week, and the adults emerge from the tunnel chewing through the barks.

Egg

The elongated white eggs appear cylindrical and a little flattened, rounded towards the ends. They grow to about 3mm (0.11 inches).

Quick Facts

Other NamesSpruce bug, spruce sawyer
Adult lifespanA few weeks
Duration of larval stage2 – 3 years
DistributionThroughout North America
HabitatPine and spruce forests
Common PredatorsBirds, and bats
Seasons active fromMay – early September
Host PlantsBlack spruce, white spruce, balsam fir, jack pine  
Diet  of larvae and adultsLarvae: Tissues of damaged or diseased coniferous species
Adults: Soft bark of the young conifer branches
Monochamus scutellatus

Identifying the Damage Caused by Them

While feeding on the bark of the twig’s undersides, the adults go on to damage the tips, making them turn red and die eventually. The larvae chew the woods and even bore holes in them to make galleries. Those created by the younger larvae on the tree’s outer bark are removable in the sawmills. However, the matured ones do more damage as they make deeper U-shaped tunnels in the wood, which is visible when the lumber is longitudinally cut. It is challenging to eliminate these galleries upon sawing the wood in the mills. Their presence makes way for fungal accumulation giving the wood a bluish tinge and reducing its value. One could find several wood chips near their tunneling spots, mostly close to the trees’ base.

White-spotted Sawyer Damage

Did You Know

  • Wood boring beetles have powerful jaws and can bite, which however does not bring in much danger to humans.
  • Of the several measures taken to get rid of these beetles is to lessen the number of dying or dead trees. In the case of the cut logs, debarking them or keeping them in the sun might reduce spots for laying eggs, thus controlling the infestation.
Spruce Sawyer

Image Source: lh3.googleusercontent.com, bugguide.net, tidcf.nrcan.gc.ca, lh3.ggpht.com

White-spotted sawyer beetle of the longhorn beetle family is a wood-boring species indigenous to different parts of North America. The white spots on the wings of both males and females earn them their name.

White-spotted Sawyer Beetle

Physical Description and Identification

Adult

Size: 20 – 25 mm (0.78 – 0.98 inches)

Color: They have a metallic black body, withwhite spots near the base of their elytra.

Other Characteristic Features: The antennae in males are twice the length of their body, while it is comparatively shorter in females. In both the sexes, a spine is seen to the side of their prothorax.

White Spotted Sawyer

Larva

Their body and head are creamy-white and reddish-brown. A full-grown larva reaches 40 – 50 mm (1.57 -1.96 inches), burrowing in the cambium and phloem upon hatching, remaining there till they pupate.

White-spotted Sawyer Larvae

Pupa

The pupae reach a length of 20 – 25 mm (0.78 – 0.98 inches), initially pale white, later turning to reddish-brown. Their legs, mouthparts, wings, and antennae are incomplete then. The appendages, too, are less prominent, eventually developing as they mature. Upon complete development, the pupae harden and become darker.  The pupation stage lasts for a week, and the adults emerge from the tunnel chewing through the barks.

Egg

The elongated white eggs appear cylindrical and a little flattened, rounded towards the ends. They grow to about 3mm (0.11 inches).

Quick Facts

Other NamesSpruce bug, spruce sawyer
Adult lifespanA few weeks
Duration of larval stage2 – 3 years
DistributionThroughout North America
HabitatPine and spruce forests
Common PredatorsBirds, and bats
Seasons active fromMay – early September
Host PlantsBlack spruce, white spruce, balsam fir, jack pine  
Diet  of larvae and adultsLarvae: Tissues of damaged or diseased coniferous species
Adults: Soft bark of the young conifer branches
Monochamus scutellatus

Identifying the Damage Caused by Them

While feeding on the bark of the twig’s undersides, the adults go on to damage the tips, making them turn red and die eventually. The larvae chew the woods and even bore holes in them to make galleries. Those created by the younger larvae on the tree’s outer bark are removable in the sawmills. However, the matured ones do more damage as they make deeper U-shaped tunnels in the wood, which is visible when the lumber is longitudinally cut. It is challenging to eliminate these galleries upon sawing the wood in the mills. Their presence makes way for fungal accumulation giving the wood a bluish tinge and reducing its value. One could find several wood chips near their tunneling spots, mostly close to the trees’ base.

White-spotted Sawyer Damage

Did You Know

  • Wood boring beetles have powerful jaws and can bite, which however does not bring in much danger to humans.
  • Of the several measures taken to get rid of these beetles is to lessen the number of dying or dead trees. In the case of the cut logs, debarking them or keeping them in the sun might reduce spots for laying eggs, thus controlling the infestation.
Spruce Sawyer

Image Source: lh3.googleusercontent.com, bugguide.net, tidcf.nrcan.gc.ca, lh3.ggpht.com

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