Published in Yard & Garden Brief, January 2000
Weevils are small beetles that possess conspicuous snouts. They are often lightbulb- or pear-shaped. When immature, the legless, grub-like larvae feed on plants. After developing into adults, some weevil species are attracted to buildings. It appears they do this to seek shelter from unfavorable weather conditions, especially when it is hot and dry. These weevils enter buildings by crawling through cracks or openings around foundations, doors, and windows. They do not harm people or pets, or damage buildings or property, or infest food products. They are just a temporary nuisance.
Strawberry root weevil, Otiorhynchus ovatus, is the most common home-invading weevil in Minnesota. These weevils are about 1/4 inch long, black or dark brown with rows of pits along their back. Strawberry root weevils do not fly. Sometimes people confuse strawberry root weevils for ticks; however they are easily distinguished, as weevils have six legs and ticks have eight.
Strawberry root weevil larvae feed on the roots of strawberries, evergreens--such as arborvitae, spruce, and Japanese yew — raspberries and other brambles, grapes and many other plants. Adults start to emerge in early summer. They feed on the edges of foliage, leaving a characteristic notched appearance.
Residents experience problems with these weevils from the end of June through August. They are attracted to moisture and are often found in sinks, bathtubs, water basins and similar places.
Other home-invading weevils
Sciaphilis asperatus is 1/5 inch long with a dark brown or black body covered with brownish or tannish scales. When these scales are rubbed off, the weevil appears to be brown with irregular blackish markings. Adults have been reported from May into November. These weevils feed at night on the leaves of sugar and red maple, yellow birch, hazel and hophornbeam. The larvae feed on the roots of these plants, although they are not considered a pest.
Barypeithes pellucidus is reddish brown and between 1/8 - 3/16 inch long. Little is know about this weevil's habits, although it appears to feed on trees. Adults are common in June and July.
The imported longhorned weevil, Calomycterus setarius, looks similar to Sciaphilus asperatus but is a little smaller at about 3/16 inch long. This weevil has a dark colored body covered with grayish brown scales. Missing scales give the appearance of irregular black patches. Adults are present in homes in July and August. Larvae feed on the roots of aster, clover, and turfgrass while adults chew on the leaves of a variety of annuals and perennials. This weevil is found primarily in southern Minnesota.
Polydrusus impressifrons is a slender 1/4 inch weevil with a dark colored body covered with lime green, sometimes irridescent-looking, scales. Weevils often appear to be green with black patches when scales are missing. This weevil is common in the northeast and north central areas of Minnesota in forested sites. Adults chew the leaves of birch, poplar, willow, and apple during June through August, while larvae feed on the roots of these trees.
Exclusion is an important step in reducing the number of nuisance weevils that enter homes. Caulk cracks and ensure snug-fitting screens and doors to reduce the number of weevils that may enter a building. Weevils, especially strawberry root weevils, are attracted to moisture and can be trapped in shallow pans of water placed around foundations or walls of the house. Although these pans captures some weevils, they probably do not capture enough to significantly reduce the number of weevils that enter homes.
Chemical control outside is usually not necessary. In instances of high numbers of weevils, home dwellers can attempt to prevent these insects from entering by applying an insecticide, such as permethrin or bifenthrin, around the home's foundation. However, the insecticides available to the public often are not very effective against weevils.
When weevils are found indoors, physically remove the insects with a vacuum or broom and dust pan. Insecticides are not effective or necessary. Remember that these weevils are harmless and temporary and will go away on their own. Their numbers can vary from year to year; because weevils are abundant one year does not mean that they will be a problem again the following year.