Weevils are a vast group of beetles belonging to the superfamily Curculionoidea, characterized by a distinctive elongated snout called a rostrum. This unique feature houses their chewing mouthparts, which they use to bore into food sources. With nearly 97,000 described species globally, weevils represent one of the most diverse groups in the animal kingdom. Their varied diet includes everything from dried, stored goods to specific parts of living plants, meaning they are found in diverse habitats, from farm fields to household pantries.
Weevils That Target Stored Grains and Pantry Goods
Weevils commonly encountered by humans infest dried food products, targeting stored grains and milled goods. Species like the Rice Weevil (Sitophilus oryzae) and the Granary Weevil (Sitophilus granarius) are primary pests in this category. They feed on seeds and starchy materials, including rice, wheat, corn, dried beans, and cereal products. Consumption can begin in the field before harvest or during long-term storage.
Granary weevils prefer whole kernels of wheat or corn and are less likely to infest fine, powdered flours. In contrast, the Rice Weevil, which can fly, is a more widespread pest capable of infesting a broader range of stored commodities. Both species cause damage by chewing into the exterior of the grain kernel and feeding on the endosperm within.
The adult female uses her rostrum to bore a small hole into a single grain, where she deposits an egg before sealing the opening. This action ensures the developing larva will have a protected and concentrated food source immediately upon hatching. An infestation can quickly contaminate large quantities of dried goods, as the weevils’ entire life cycle, from egg to adult, occurs within the food itself. The consumption of these stored products constitutes a significant source of loss in commercial storage facilities and residential kitchens.
Weevils That Feed on Living Plants and Crops
The majority of weevil species are herbivorous, consuming various parts of living plants and often specializing in a single host or narrow group of plant species. They are categorized based on the specific plant part they target, which determines the damage caused to crops and ornamental plants. Many species are root and stem feeders, with larvae developing entirely underground or inside woody tissue. The larvae of the Black Vine Weevil, for example, feed on the roots of woody ornamentals such as rhododendrons, yews, and azaleas, often girdling the crown and causing the plant’s death.
Other weevils are bud and fruit feeders, focusing on reproductive structures. The Boll Weevil (Anthonomus grandis) targets the cotton plant, where the female lays eggs inside the flower buds or young fruit (bolls). The developing larva consumes the internal contents of the bud or boll, leading to its destruction and preventing the formation of cotton fiber. Similarly, the Plum Curculio (Conotrachelus nenuphar) is a pest of stone and pome fruits, including peaches, plums, and apples.
The adult Plum Curculio chews small, round feeding holes into the developing fruit surface, and the female creates a characteristic crescent-shaped incision where she lays her eggs. Once the eggs hatch, the larvae tunnel and feed within the soft fruit flesh, causing the fruit to drop prematurely. A different group of species is specialized to feed on seeds and nuts, such as the Filbert Weevil, whose larvae bore into and consume the internal contents of acorns and hazelnuts.
Larval Versus Adult Feeding Strategies
The feeding habits of weevils change as they progress through their life stages, shifting between the soft-bodied larval form and the hard-shelled adult form. The larvae are typically the most damaging stage, distinguished by their internal, concealed feeding strategy. They require soft, nutrient-dense tissue, which they find by feeding from the inside of a food source, such as burrowing within a grain kernel, tunneling through a plant stem, or eating the tissue of a plant root.
Adult weevils usually employ an external feeding strategy, consuming the exposed parts of their host plants or stored goods. Adult root weevils, such as the Black Vine Weevil, feed on the edges of leaves, creating distinctive, notched patterns. Adult fruit weevils use their snouts to pierce the skin of fruit to access the pulp beneath. Even in stored product pests, the adult Rice Weevil feeds on the exterior of a grain kernel, though its most destructive act is boring a hole for the internal-feeding larva.