The sound of scurrying feet coming from the attic at night could mean you have rats, mice, raccoons or other nocturnal visitors, but if you hear the sound during the day, your guests are probably squirrels. Squirrels nest in attics to seek shelter from the elements and to give birth and raise their young. They can spread disease and damage electrical wires, so it's best if you encourage them to leave.
Even though squirrels are famous for hoarding supplies of nuts and seeds, the ones in your attic will still leave in search of food and that's your chance to close the door and lock it. This strategy requires a careful appraisal of all the holes, gaps and cracks through which a squirrel could enter, and closing these entrances -- except the main one -- with caulk, steel plates or screens. The main entrance may be obvious; it may be large, and you may notice evidence of use. If it isn't obvious, watch the attic until you see a squirrel entering or leaving the attic.
Guarding the Main Entrance
Once you have sealed all entrances but one, your job becomes easier. One method of exclusion is to install a spring-loaded door on the main entrance that allows the animals to go out, but doesn't allow them back in. You can also set a live trap outside the hole, either by securing it to the roof or attaching it to the soffit. There's no point setting the trap in the attic, says squirrel control specialist David Seeveld, because squirrels never enter traps inside the attic. He also advises that placing repellents such as mothballs inside the attic usually has little effect.
Mothers with Babies
The problem of squirrel control becomes complicated by the presence of babies, because they are dependent on the mother and will die if you trap or exclude her. The mother usually gives birth within one to two weeks after entering the attic, and the young are vulnerable for about six weeks. After that, they can leave on their own. Since it usually isn't practical to go into the attic and look for a nest, it's a good idea to wait for six to eight weeks after you first notice the presence of squirrels before taking steps to exclude them. That way, you'll avoid the odor and contamination that the squirrels will cause if they die in the attic.
Trapping as an Alternative
Excluding the squirrels from the attic with a one-way door is the most humane and effective way to deal with them, but if your house is wood and in disrepair, they may chew their way back in. Trapping them may become necessary. You can purchase body grip squirrel traps, which are like oversized mouse traps, but they are difficult to set and dangerous. Placing live traps outside on the roof is a better alternative, but you should contact a pro to relocate the animals you catch. Loading the traps in your car and relocating the squirrels yourself is illegal in most states.