Spruce budworm larvae have black heads and greenish-brown bodies that are lighter on the sides. They usually have two rows of whitish spots along the back. They tend to be wasteful feeders. Instead of eating the whole needle, they bite off the needle at the base. The needles are left hanging in a mass of silk.
Damaged trees have a characteristic, reddish-brown colour.
Yellow-headed spruce sawfly larvae have a yellowish or orange head with a light yellowish green body. The body has gray green stripes running lengthwise. Damage first occurs on new needle growth. As the larvae grow, they consume the older needles. They can completely strip trees.