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Insects and other arthropods

White-spotted sawyer

Monochamus scutellatus

Tabs group


These beetles are recognizable by their black colour and the small white spot formed by the scutellum (the triangle at the base of the elytra). They have strong, long, reddish legs. The females are larger than the males, and their elytra (wing covers) often have small white spots. Their antennae are barely longer than their bodies, whereas the males’ antennae are twice as long as their bodies. Without their antennae, the insects vary in length from 13 to 27 mm.

The legless larvae are whitish and slightly flattened, with brown heads. They can grow to more than 4 cm long.

Life cycle

It generally takes two years for these insects to develop completely, except in the southern part of their range. The adults emerge and mate in the spring.
The females find a host plant, ideally in a sunny spot, and lay their eggs in the summer in the niches they make in the trunks of weakened or dead conifers. The larvae that hatch make tunnels on the surface, boring more deeply into the wood as they grow. They winter in these tunnels in the first year. Then they bore even more deeply into the wood in their second year, making U-shaped tunnels as they head back toward the surface.

Once near the surface, the larvae clear some space for themselves in the wood to create a cell where they spend the winter in the form of prepupae and then pupae.
The adults emerge the following spring, after using their strong mandibles to make a circular opening in the bark.

Geographic distribution

They are found in Alaska, throughout Canada, and in much of the United States. 

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