If you're like most homeowners, you've had to deal with utility installation at some point. Whether it was a new cable line, Internet service or phone wiring, the installers likely ran the lines into your home through holes drilled in the exterior walls. The more conscientious installers may have added sealants or caulk around these lines on your home's interior, but what about on the outside? Most likely, there are at least some utility or pipe penetrations in your walls that are surrounded by large gaps, providing an open invitation for insects.
Some common types of through wall penetrations include those made for water, gas, electrical or air-conditioning piping. Check the entire exterior of your home for these types of openings, as they may be located at either ground level or along the roof line. Often, you can visually follow cable and telephone lines from outside poles to find the path they take into your home. Don't forget to check around outdoor faucets and electrical outlets [source: Gouge et al].
Fill smaller gaps or cracks using pipe sealants or caulk. For larger openings, look for expandable polyurethane foam. Some installers prefer to add copper mesh or steel wool as a base layer behind this foam to deter insects that may bore through [source: Potter].