Mud daubers gather mud, roll it into balls and form small dirt nests like the one seen here.
Mud daubers collect mud for their nests and deposit it inside furnaces. Once hardened, the nests act like shards of pottery inside a running furnace. This is when damages occur.
Mud Dauber Screens protect your furnace by preventing mud daubers as well as spiders, wasps, birds and other small animals from entering through open vents.