You may not know it from the number you see in your home, but ants generally reside outdoors. That means that when you see a trail of ants leading to your kitchen garbage can, they came in from some kind of crack or crevice, and the likely culprits are your windows. Ants are tiny creatures and it doesn't take much space to get through when you're marching single file. Especially in older homes, whose windows tend to have more tiny cracks and openings. If you see a trail of ants in your home, follow the path backwards and there's a good chance that it leads to a window.