Ground beetles are very common "outdoor" insects that occasionally become pests by wandering into houses and buildings by mistake. They do not damage household structures or furniture and are harmless to people and pets.
There are hundreds of species of ground beetles commonly found in Iowa. Most of these are about 3/4 to 1/1/4 inch long though smaller species may be present. Most species are shiny black with few distinctive characteristics aside from the lines or ridges down the wing covers. A few species have brightly colored sections or spots.
Ground beetles live on the ground under leaves, logs, stones and other debris. They are beneficial because they feed on insect larvae. They feed mostly at night, and may be attracted to lights. They usually gain entrance to the house by crawling in through small cracks or openings, or through open doorways and windows.
Controlling ground beetles is usually not necessary. Exclusion techniques to prevent entry include caulking gaps and cracks in the foundation and siding, or repairing windows and screens. In severe cases you could attempt to reduce outdoor populations by eliminating their outdoor hiding places. As a last resort it may be worthwhile to treat hiding places, the foundation and building perimeter with a residual insecticide such as diazinon or Dursban. The only effective control for ground beetles already inside is to pick them up and discard.
This article originally appeared in the June 3, 1992 issue, p. 93.