Contact poisons are absorbed by bugs when these are sprayed or are picked up by crawling insects on sprayed surfaces. Examples of these are aerosol and liquid sprays.

When sprayed on surfaces, these products leave an invisible coating deadly to pests that may last for weeks. Such products can also be used as a space spray to control flying insects.

Once sprayed high into the air in a closed room, they leave a chemical mist that kills all exposed bugs. Fortunately, that mist doesn't linger longer enough to affect humans or animals.

If the pests in your home are beyond the reach of contact poisons, they can be eliminated by stomach poisons. Unlike aerosols, these surface or residual products persist beyond the moment they are applied and can continuously kill insects.

For stomach poisons to work, they have to be eaten by pests. These are commonly used in baits and bait traps. The traps are usually placed in cupboards, under sinks, and other possible hiding places of insects. The baits are either consumed on the spot or are carried by bugs to the colony.

The poisonous powder in baits may also adhere to the bodies of insects and reach the stomach when the pests groom themselves. This form of insecticide can control bugs for as long as three months depending on the kind of bait used and the type of infestation your home has.

Other residual products make use of inhalation poisons that affect insects once they are breathed in. These fumigants are often sold as coils and mats which release toxic gasses that choke out insects.

But don't be alarmed since the gasses are non-toxic to humans and the fumigants emit no harsh odor or irritating vapors. The device is either lighted in the case of coils or plugged to an electric outlet. It can knock out 80 to 100 percent of mosquitoes in a 20-square-meter area within 30 minutes. A single mat can last for eight hours. (Next: Guide to safe insecticide use.)

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