Direct Spraying

• Broad-spectrum insecticides generally perform well against spiders. These can be purchased in large amounts and applied through pump-action sprayers. The key to controlling an infestation by direct spraying is regular application. All corners, especially ones away from regular human traffic, should be sprayed daily until the number of spiders begins to decrease. This is a good way to sharply reduce the number of spiders in your building, and can be used in conjunction with long-term control methods to keep the numbers down. Direct spraying is a short-term solution, and without taking further steps the spiders will return in short order.
  
  

Fumigation

• Fumigation is a more effective version of direct spraying. By using either commercially available bug bombs or a professional fumigation outfit, you can kill all the spiders in a building simultaneously. This can be tricky in a large building, since the effectiveness of bug bombs is limited by the volume of the space you are fumigating, and professional fumigators may charge a great deal of money to fumigate large buildings. However, if you have the resources and need a quick solution, fumigation is the best way to destroy the spider population in your building. Just make sure you implement some long-term controls, since fumigation is also a short-term solution, and does not prevent new spiders from moving in.
  
  

Barrier Treatments

• A barrier treatment is a poison that is sprayed around the foundation of a building and in common entry points such as windows. It is an effective method of controlling many pests, since a relatively small amount of pesticide can kill every pest that tries to enter the building, and it remains effective for two to three months in most cases. It is especially attractive for large buildings, since the perimeter of a large building is proportionally much smaller than its volume. However, barrier treatments have a limited effect on many spider species since they do not often come into full-body contact with the ground. A barrier treatment is a cheap method to reduce, but not eliminate, the number of spiders entering a building.
  
  

Environmental Controls

• This is the most effective method of keeping spiders from returning to a building once you have cleared it out. While it is not a quick fix on its own, eliminating the environmental factors that attract spiders to a building will eventually eliminate the infestation. Make sure all entrances are properly weatherproofed and that there are no gaps in the building's insulation. For most buildings, a single unsecured entry point can be the source of an entire infestation. Filling wall cavities with foam insulation can deprive spiders of places to hide and breed. Finally, replacing outdoor lights with special "bug lights" that don't attract flying insects will remove the food source that likely attracted the spiders in the first place. Eliminating modes of entry, places to hide in your building, and a steady food source is the most effective method of long-term control.