Sawflies are strange little caterpillars which do not visually resemble their name. These little green caterpillars with shiny black heads begin to show up, sometimes by the thousands, on a single susceptible tree or bush early in the spring. Their first appearance usually coincides with the flowering of Crabapple trees. These insects ‘rear their little heads’ most commonly on Scotch, Austrian & Mugho Pines.
Sawflies are hard to spot when they first hatch as they are smaller than the head of a pin and camouflage themselves by matching the color of the pine needles that they plan to devour. Within 6 weeks of hatching they quickly grow to over an inch long as they continually feed and damage the host plant. They develop into moths, mate, and then redeposit their eggs on their favorite plants. These eggs ‘overwinter’ extremely well and the process begins again the following year.
Homeowners who do not notice these insects at first are often shocked when they walk by the tree or bush, as this startles the insects. The plant seemingly 'jumps to life' as the hundreds or even thousands of Sawflies snap to attention in unison!
Mugho Pine bushes and Scotch and Austrian Pine trees can be severely damaged if not completely devoured. Usually much of the damage is permanent as the inner needles never re-appear. The plant can appear very thin and sparse until much later, after several years of new growth rebuilds the plant.
Sawflies are one of the easier insects to control as a variety of insecticides are effective against them. The problem however is that homeowners don’t usually treat their susceptible plants until the insect is clearly visible, and that is usually after they are full grown and much of the plant is damaged. Once you find Sawflies in your landscape plants it makes sense to treat them on a yearly basis, long before you notice their presence.