Stored improperly, schach can become a target and breeding ground for insects. These insects could then drop onto the table and into your food.
When schach is wrapped in plastic or any similar non-breathing material, ambient temperature changes may lead to development of condensate inside the wrapper. This can create a moist environment ideal for breeding insects.
People tend to keep schach mats in their original bags and then store it in areas that are not climate-controlled (e.g., basement storage rooms, garages, sheds). These types of conditions often lead to infestation.
While we do not have statistics to show how often schach is infested, it would seem prudent to prevent schach infestation by not storing it in plastic. If you must wrap it, use paper, or leave the plastic open so it can vent. Under dry conditions – whether temperatures are cool or hot – insects won’t thrive.
If you are concerned your schach may be infested, take advantage of some sunny days before Sukkos to dry it out. Unroll it and leave it out in the hot sun. A few days of exposure to the dry heat, followed by shaking the schach out, will rid the schach of possible insect problems.