Federal Pest Control technicians will again treat the external walls, wall cavities; outdoor furniture and roof voids of a house, however in the case of non-webbing spiders it is important to note that the pesticide must land directly on these spiders to kill them. That is why we place so much emphasis on thoroughly dusting the roof void and wall cavities. The “cloud” of dust floats throughout the entire roof void and wall and any spiders in those areas will be killed by “breathing” the dust.