Specific inorganic silica gels are used as an adsorbent drying agent for controlling insect pests in a structure. When it is too humid in the structure, the silica gels adsorb moisture. On the other hand, when it is too dry in the structure, the silica gels supply moisture. The silica gels thus create the environment where household insect pests cannot survive. Moreover, by exposing invading insect pests to silica-gel particles, the pests' tissues are physiologically decayed, and the population density of the insect pests is decreased. Insect pests in the structure can be thus controlled using the silica gels.