Chances are you get occasional houseguests you’d rather not have visiting. While I can’t help you with the two-legged kind (though putting them to work often helps move them along), I can offer advice for dealing with pests of the insect variety—without resorting to nasty chemicals that are bad for you and the environment, OR spending a mint to eradicate the little buggers.
As a general rule, your first line of defense is to keep pests out by sealing cracks, using repellents, screening openings, and not bringing any stowaways home. Should any make it inside, most of them can be trapped pretty easily if you have the right bait, like their favorite foods or natural critter-specific chemical attractant scents called pheromones.
About this time of year, I often have some small kitchen guests. It’s an inevitable fact of spring: Sugar-seeking ants find their way in through some infinitesimal crack and start casing the joint. Once they find crumbs or other spilled food, the news spreads like wildfire through the colony, and soon there is a tiny two-lane highway full of ants carting away my leavings.
Reduce your chances of an ant invasion by keeping spills cleaned up and food stored in secure containers. Seal any cracks with caulk and sprinkle entry areas with crushed dry mint, ground cinnamon, or cloves to keep them out. Also, clean the floors, counters, or any other surfaces where you’ve spotted them as often as you can, so you’ll remove the trails that they lay down to lead their fellows to the food.
If you can’t stem the invasion that easily, you can use a sugar-borax paste to control the ants. Borax is reasonably safe for humans (you still don’t want to eat it, or allow kids to play with it, so keep it off food and out of reach of little hands), but when the ants carry it back to their colony, it kills the whole nest. Mix 1 teaspoon borax or boric acid and 1 teaspoon sugar or honey with enough water to make a thin paste, and put the mix in a small jar near where the ants have been foraging. Refill as needed until it no longer disappears. You can also buy ready-made liquid natural ant killer that contains borax and sweetener.