The adult Craesus septentrionalis has a chestnut brown posterior section of the abdomen and a black head, thorax, and anterior part of the abdomen. Clear wings are present.
Near the feet, the legs are wider than they are close to the torso. The larva is slim and greyish-green in color with a black head, yellow collar, and longitudinal rows of black dots.
Host plant:
Consumed birch foliage includes paper, black, yellow, and grey birch and several other varieties. These group-feeding caterpillars, which are most prevalent at leaf margins, have the potential to defoliate small trees.
Damages caused by Dusky Birch Sawfly:
They start by progressively stripping the leaves of their flesh since the young larvae won’t consume the veins. As they age, they start eating in groups and finish the entire leaf. Defoliation can affect whole bushes or trees.
Life history and Habits:
There are one or two generations every year. Prepupas spend the winter in a cocoon under the ground. Pupation takes place in the spring, and adults appear in May. From April to May (1st generation) and then again from mid-July to mid-September, eggs are deposited, and larvae emerge (2nd generation).
