2017 has been a busy year for home-invading insects. One of the invaders we have been receiving numerous reports of are small, black insects that are often observed crawling up bathroom walls, hanging out in basements, or otherwise finding their way inside. After a little investigation, the insects in question are either root weevils (Figure 1) or the imported longhorned weevil (Figure 2).
Weevils (Family Curculionidae) are a kind of beetle (Order Coleoptera) that is characterized by a distinct snout on the front of their head, with antennae that originate halfway down the snout. Root weevils are members of the genus Otiorhynchus, and there are at least four species in South Dakota; the strawberry root weevil (Otiorhynchus ovatus), the rough strawberry root weevil (O. rugostriatus), the lilac root weevil (O. meridionalis) and the black vine weevil (O. sulcatus). The imported longhorned weevil (Calomycterus setarius) is similar in size to root weevils, but is a mottled gray color instead of black.
Appearance & Behavior
The five weevil species are very similar in appearance and size. Adult root weevils and the imported longhorned weevil are approximately 1/3 of an inch long. The root weevils are black in color whereas the imported longhorned weevil is mottled gray. The adults of these weevils do not fly, and will sometimes play dead if disturbed. Identification to species is not necessary for management since they are similar in behavior.
Root weevil adults feed on many plants in the landscape but appear to prefer lilac leaves and yews. Both of these plants are abundant in residential landscapes. Their larvae feed on the roots of a variety of plants. The mature larvae overwinter, pupate in the spring, and new adults emerge around June. Imported longhorned weevil adults feed on a variety of plants, but are noted for their presence in soybean.
Management for root weevils or imported longhorned weevils that find their way indoors is the same regardless of species. Since they do not feed or reproduce inside structures, the best course of action is to sweep or vacuum them up. To prevent future invasions by the root weevils (or other insects seeking shelter inside) check around doors and windows for any possible entry points. These insects are considered nuisance pests indoors, and their presence could be an indication of a large outdoor population. To determine if plants around the home are being fed on examine them for “saw-toothed” leaf edges, which are characteristic of feeding due to these weevils.