Identification
Pour reconnaître le longicorne noir, on regarde trois choses : le point blanc unique à la base des élytres, les antennes grises très longues (presque deux fois le corps chez le mâle) et le corps noir moucheté de gris. C’est ce point blanc unique qui le distingue du longicorne asiatique, couvert de nombreuses taches blanches et aux antennes annelées de blanc.
Antennes et trous ovales
Antennes très longues chez l'adulte, gros trous de sortie ovales et copeaux grossiers chez la larve: le longicorne se distingue nettement des petites vrillettes à trous ronds.
-
AWhite spot on the scutellum
A single, clearly visible white spot at the base of the elytra, just behind the pronotum. This is the diagnostic feature of the white-spotted sawyer.
-
BVery long antennae
Greyish antennae that can reach up to twice the body length in the male; somewhat shorter in the female.
-
CFlecked black body
Matte black body with a bronze sheen, flecked with small grey markings, and a pronotum bearing a spine on each side.
Adult
Emerges from the wood in spring or summer; lives a few weeks, long enough to mate and lay eggs in the bark or in cracks in the wood.
Life cycle
HOLOMETABOLOUS · 4 STAGES · 1 TO 3 YEARSThe female lays her eggs in notches chewed in the bark of recently dead, felled or weakened conifers (pine, spruce, fir).
The larva tunnels through the wood for 1 to 2 years, feeding on the dead wood. It is the larva that produces the chewing sounds.
Pupation takes place in spring in a chamber under the bark or in the wood.
The adult emerges in summer through a round exit hole and lives a few weeks. It is often attracted to light.
Do not confuse
Confused with other wood-boring insects that leave exit holes.
Asian longhorned beetle
A regulated invasive species: glossy black body with large white spots and antennae banded in bluish white. Must be reported to the CFIA. The white-spotted sawyer, by contrast, has only a single white spot and grey antennae.
Northeastern sawyer
Another Quebec Monochamus, larger, with a mottled grey body. Same habits (dead conifers) but paler, mottled colouring.
Signs of activity
Round exit holes
Circular exit holes 6 to 10 mm across in firewood or conifer logs
Coarse frass
Coarse sawdust (frass) near the infested wood, a sign of larval activity
Adults on the wood or near windows
Adults seen on firewood brought indoors or drawn to light sources in the evening
Most longhorn beetles attack damp, bark-covered wood or firewood; well-dried structural lumber is rarely affected.
Treatment
Drying and inspecting the wood
- < 20 % Properly dried wood Wood below 20% moisture discourages the larvae
- Store the wood sheltered, raised off the ground and well ventilated, and inspect each piece before bringing it indoors; have a professional treat the structure if it is affected.
If oval holes appear in beams or joists, have a professional assess the situation
Burn infested firewood promptly rather than storing it near the house
Finding the infested wood
Follow the holes and the frass
Examine firewood, framing, antique furniture and bark-covered wood for oval holes
Find the piles of coarse shavings that indicate recent larval activity
Take infested firewood back outside; for structural wood, call in a professional
Prevention
- Bring firewood in only just before burning it
Avoids storing conifer firewood indoors for long periods: adults can emerge from it
Indoors - Debark and dry the wood
The white-spotted sawyer develops mainly in freshly dead wood that still has its bark
Outdoors - Inspect conifer wood
Check for round exit holes and sawdust before bringing logs inside
Outdoors - No concern for the structure
The white-spotted sawyer does not reinfest the dry, finished wood of a house
Indoors
Frequently asked questions
Is the longhorn beetle dangerous to people?
No: it does not sting and does not bite in any meaningful way. Impressive as its long antennae are, it remains harmless to people.
Does it attack the wood in my house?
The white-spotted sawyer develops in freshly cut or weakened conifers, not in dry, finished lumber; it does not infest sound framing.
Why am I seeing them indoors?
One sometimes emerges from a log of firewood brought inside, or comes in through an opening, drawn by the light. Its presence is usually temporary.
What should I do?
Take the suspect firewood back outside and have the situation assessed if there are holes and sawdust in a structure. An exterminator can tell active feeding from old galleries.