There are a variety of reasons pests like your attic, and they vary depending on the pest we're talking about. The biggest and most universal reason is that your attic is secluded from the rest of the house. Bugs and wildlife like to think your house is their house, and they don't much care for you being around. To be specific, you freak them out. Let's take a look at this problem together and see if there is something we can do about it.
Who likes my attic, and why?
Wasps. Many wasps, especially yellow jackets, love man-made structures, especially the quiet spaces of an attic. An attic offers shelter from the elements and is a nice dry place to build a nest. For an insect that likes the shelter of eaves and overhangs, having four walls is even more attractive.
Termites. Your attic is attractive to termites because of the ample food sources. They don't just eat the wood your home is made of, they like furniture, paper and other wood products.
Cockroaches. You'll find roaches breeding in your attic because of the stillness. They will be found in the corners and tucked in cracks. Roaches prefer to be in crevices because they like it when their chest and back touch their surroundings. Sort of an anti-claustrophobia.
Insects in general. If you have a cluttered attic, you'll have all sorts of insects, including insects that could care less if humans are around, like the spider or the centipede.
Bats and birds. If you have an older house, you'll have larger critters trying to squeeze in. Flying pests are the most likely because they can easily reach rotted holes or broken windows. To these pests, your attic is attractive because they can easily get in and out.
Mammals. There are a variety of mammals that love attics. Here is the short list: squirrels, rats, mice, snakes, hedgehogs, opossums and raccoons. These furry, disease- and parasite-carrying creatures all love your attic because it is better than living in a hole or the hollow of a tree, especially when the cold weather comes.
So what can I do about all these critters living in my attic?
Just as there are a variety of pests that want to get in, there are a variety of ways to keep them out. Repairing rotted holes, fixing windows, locking windows, cutting back tree branches from the roofline and putting pointy wire at the end of power lines will go a long way to keeping mammals out of your attic. To keep the bugs out, you'll need to seal smaller holes with a caulking gun, reduce clutter in your attic, and keep it dry and well ventilated. Talk to a professional pest control company about other exclusion methods specific to your situation and see about getting an attic treatment. Your goal should always be to make your home and attic unattractive to pests. That is a major step in living pest free.