Question
WHILE PAINTING I FOUND A SOFT SPOT IN THE WALL WHERE THE SHEETROCK WAS MISSING FROM BEHIND THE PAINT.  AFTER SCRAPING OFF THE PAINT I FOUND TRAILS IN THE SHEETROCK & LITTLE CUBBY HOLES.   THERE WAS A POWDERY RESIDUE, BUT NO SIGN OF CRITTERS.  NO SIGN OF MOLD OR MOISTURE.  DO I NEED TO TREAT WITH PESTICIDE BEFORE REPAIRING THE DAMAGE.  SHOULD I BE LOOKING FOR WHERE THEY WENT?

Answer
Dino,

I don't know of any insect that specifically targets sheetrock. The only one that might damage sheetrock like this would be carpenter ants. As carpenter ants expand their nest they will excavate whatever is in the way. If you are not familiar with this large ant take a look at this page http://www.livingwithbugs.com/carpenter_ants.html and pages linked to this page.

I'd investigate a little more before applying any pesticides. If you can look inside the wall (is this an exterior wall with insulation?) check for evidence of ants.

Is there any evidence of tooth marks caused by a mouse?

Also, post a picture in a follow up if you can.

Jack DeAngelis, PhD
Extension Entomologist (ret.)
author Living with Bugs: http://www.livingwithbus.com/bug_book.html