While spiders are typically of no harm to humans, they are indeed unwanted by most. The sure sign of spiders are clearly their webs. Knocking down webs as soon as they are spotted will help in discouraging them to nest there. Another spider that causes alarm is the wolf spider. These spiders are active hunters and do not build webs. The biggest reason spiders invade a structure is to feed on insects that are already present. To help with elimination, windows and doors need to be properly sealed on the inside and out.