Plants and their corresponding insect pests have had all summer to grow. When they were small and developing, it was easy to overlook them.
I hadn’t noticed a dogwood sawfly population explosion building in my yard until just this week. The larvae are nearly full size and it was surprising to come across them. These insects look and act very much like caterpillars but they’re not. Instead, they are the larval stage of a wasp-like insect.
The female sawfly lays her eggs into a dogwood leaf in rows along a leaf vein. The larvae hatch from the eggs and begin voraciously feeding immediately. The youngsters eat the soft parts of the leaf leaving the veins behind. This causes a pattern on the damaged leaves called windowpaning. Later as they grow bigger and their mouth parts get stronger, they will eat all of the leaf except the tough mid-vein.
All of the larvae that hatched from the clutch of eggs stay together during their developmental stages. So many worms feeding in the same area can often defoliate an entire plant.
If I was watching a little more closely, I could have applied an insecticide when the larvae were small and easy to control. But now, the damage to the plant has been done and the larvae are much harder to kill. Normaly, an infested dogwood will recover from a sawfly attack without any lasting damage.
Soon, as they reach full size, the larvae will begin to crawl off of the tree and onto the ground looking for a place to overwinter as pupae. They look for wood to burrow into and make a pupal case. Usually it is just pieces of branches that they use but occasionally they will make trouble by boring into landscape timbers or even wooden siding.
Wood siding can be damaged by the just the insects themselves making holes. However, even more damage can occur if woodpeckers start pecking holes in siding looking for sawfly larvae and pupae to eat.
Keep an eye out for them a little later in the season, sometimes you can see them crawling on sidewalks or on deck rails looking for just the right spot. They can be sprayed but it’s easy to just step on them or scoop them up and destroy them.