The following pictures are NOT of a SIP panel. They are pictures of a sheet of 2 inch EPS that was stored for twenty years in the woods near my home. They are meant to provide you with an idea of what an ant infestation could look like inside a SIP panel.
These were your typical ants, they were not carpenter ants. There were 4 separate sheets of 2' x 4' x 2" EPS stacked on top of one another on the forest floor. The ants did a fairly complete job of excavating the foam. This data contradicts what I've found elsewhere on the web. A typical question and answer statement is, "Q. Are ants a problem in SIP construction. A. No more than in typical construction."
I don't think ants will destroy the R-value of fiberglass like they've destroyed the R-value of these pieces of foam.
***Please understand that these panels were in the worst of conditions. They were covered with leaves, sitting on a moist forest floor and were there for 20 years. Your SIP panel will never be exposed like this. However, if your home is exposed to conditions that make an ant infestation possible, it might be a good idea to have your home inspected regularly by a reliable pest exterminator.
These are thumbnail images, click to see a high resolution image.