When faced with an invasion of insects, the first thing to do is to determine if this is a variety of insects that are easy to deal with yourself or do they require a professional. For instance it is important to distinguish between insects that migrate in and out of the house and hence can often be cut off with simple products like diatomaceous earth, which is a non-toxic power that scratches the unprotected bellies of crawling critters, which causes them to dehydrate and die -- and insects that create nests inside your walls, like carpenter ants, and you need a professional capable of getting to the queen.
IDENTIFY THE ENEMY
If you are faced with ants, it is a good idea before panicking too much to know if you really have carpenter ants or some other type of ant before going too far, certainly before you start ripping open walls. Start by trapping one of the ants and then take a close look at it with a magnifying glass. The University of California has a great little interactive web site that will allow you to Identify your Ant. If find you have carpenter ants, get more information here. To help you identify insects in general RAID has a great little Identify Your Bug guide on their website.
To avoid the expenses of a professional for something simple, capture one of the insects in a jar, preferably alive and not squashed. If you see two or three "varieties" such as some with wings and others without wings, they may be the same species or two families visiting at the same time; capture samples of everything you see. If you don't feel capable of catching them, place fly paper in their path, they should be there waiting for your examination the next day. Then either use the internet to identify the critter, or take it to a professional exterminator shop. This is usually better than taking it to the local hardware store, simply because of the difference in experience and qualifications of the person behind the counter. Now you can get advice specific to your unwanted visitors, and only spend the money you need to spend.
Many people want to do battle themselves and send me a lot of experiences. I will be putting what appear to be the most promising here.
RAID has a product called Ant Killer that is a gel that comes in a little red bottle, designed to place drops of posion either right on the top of an ant-hill or in the path that leads into your house. A good number of our visitors have said this is a very effective poison designed to be carried back to the queen and wipe out the colony.
ORTHO had a disposable battery powered spray wand with their 4 Litre container of Ant Begon Max. This is extremely useful for walking around the house putting a band of spray on the concrete foundation all around, cutting off the paths of all insects. I use this every year as preventitive maintenance after finally getting rid of carpenter ants in my walls.
Diatomaceous earth is a non toxic powder that kills most crawling insects because as they crall over it, the very small but sharp particles in the fine powder scratches their bellys and absorbs lipids from the waxy outer layer of insects' exoskeletons, causing them to dehydrate. This stuff will not harm pets -- unless of course you have a pet cockroach.
The company PowderTrap has a series of traps (Cluster flys, Lady bugs, small ants) that use very fine ground up egg shells that act like quicksand and drown hundreds of insects. The cluster flys fall into the window sill traps, the lady bugs and small ants follow a sent to get trapped. These traps work incredibly well but I have only found them on the web.
HOME MADE RECIPES
Several people report having good results with various combinations of sugar and baking soda -- the most effective appearing to be ICING SUGAR AND BAKING SODA in a 50/50 mix. Al from London Ontario even reports having gotten rid of carpenter ants with this.