Frass refers to debris left by insects. Although the word is sometimes used by beekeepers to refer to fecal droppings, frass also refers to the material left behind by boring or chewing insects. A good example is the sawdust left by carpenter bees or termites. More often than not the debris left by insects is a mixture of chewing debris, excrement, and insect body parts.
“He called an exterminator after finding piles of frass in the crawlspace.”