The foreign grain beetle feeds on molds that sometimes occur inside walls of newly built homes. During construction, moisture invariably wets wood and becomes trapped in walls thereby allowing molds to grow. The beetles find this mold and begin breeding, then months or even a year later, the adults start emerging, sometimes in large numbers. Eventually, the walls dry out, the molds die and so do the beetles. In the meantime, treatment beneath baseboards and the voids behind electric outlets using a dry residual dust product can reduce the numbers of beetles seen. You may wish to hire a professional to positively identify the beetles involved and to make treatment recommendations.