Definition of willow sawfly
: any of numerous sawflies that infest the willow: such as
a
: a large American sawfly (Cimbex americana) whose larva is pale greenish with a black dorsal stripe
b
: a steel-blue sawfly (Dolerus arvensis) or a related smaller brownish fly (D. bicolor)
c
: a black sawfly (Nematus ventralis) whose yellow-spotted blackish larva infests also the wild cherry
