We are plagued with catapillars that come through the cracks in the concrete in front of our office building and into the building lobby.
Answer
Since this is a public building, you need to be a certified pesticide applicator with liability insurance to apply any insecticide. The life cycle of insects that go through the caterpillar stage is eggs that hatch into larva (caterpillar). The caterpillar feeds usually on leaves and then forms a pupa which becomes an adult flying insect through metamorphosis. Adults lay eggs. The eggs are destroyed with horticultural oil. The caterpillar can be treated with insecticides on their food. Usually a systemic insecticide is used since it persists in the food for a length of time. Sticky traps can be used to physically catch the caterpillar and then remove them. Stikem and tanglefoot are two brands. Bacillus thuringiensis (bt) is a bacterium that can be used to treat most caterpillars on trees and shrubs, but it must be renewed weekly until the caterpillar disappears.
The identification of the insect is the first step. Then researching the life cycle will indicate where and when it should be treated. Since we will encounter freezing weather shortly, you may chose to let nature resolve your problem this year and take corrective action in late winter Or early spring.