Weevils are a diverse group of beetles, recognizable by their distinctive elongated snout, also called a rostrum. These insects are small, with most species measuring less than a quarter of an inch, and are herbivores. Weevils do not bite people or household pets for feeding or defense. They are pests of plants and stored dry goods, not mammals, and their anatomy is not designed for biting skin.
Weevils and Biting Behavior
The reason weevils do not bite humans relates directly to their specialized anatomy and feeding ecology. The weevil’s most prominent feature, the rostrum, is essentially an extension of the head, and it is at the very tip of this snout that the chewing mouthparts are located. These mouthparts feature mandibles that move horizontally. Weevils use this structure to bore into solid plant material, such as seeds, nuts, or grain kernels, to feed and lay their eggs. This mechanism is highly adapted for excavating tunnels into hard substrates, not for piercing skin or drawing blood. When threatened, weevils instinctively scatter, play dead by tucking in their legs, or attempt to fly away.
Understanding Weevil Damage
Since weevils pose no physical threat to people, the damage they cause is entirely related to property and food destruction. Weevils are categorized as agricultural pests, attacking crops in the field, and as stored product pests, infesting dry goods in pantries and storage facilities. The most significant harm occurs when female weevils lay their eggs directly inside a food source, such as a grain kernel. The resulting larvae hatch and consume the grain from the inside out, contaminating the remaining product with their presence and waste. This internal feeding significantly reduces the quality and weight of stored products like rice, corn, and wheat, leading to substantial economic loss. Outdoor species, such as root weevils, have larvae that feed on plant roots, which can stunt growth and ultimately kill garden shrubs and ornamentals.
Common Types of Weevils Encountered
The types of weevils encountered vary depending on the environment, but several species are commonly found in and around homes. Pantry infestations are usually caused by the Rice Weevil (Sitophilus oryzae) or the Granary Weevil (Sitophilus granarius), both of which target stored grains. The Rice Weevil is a strong flyer with four reddish-brown spots on its wing covers, while the Granary Weevil cannot fly and is uniformly darker brown to black. Gardeners often encounter the Black Vine Weevil (Otiorhynchus sulcatus), a flightless species whose adults chew distinctive U-shaped notches into leaf edges. Its larvae are destructive, living in the soil where they feed on the roots of ornamental plants like rhododendrons and hostas, causing wilting and plant death. In agricultural settings, the Boll Weevil (Anthonomus grandis) is known for damaging cotton crops by laying eggs in the flower buds and bolls.
Control and Prevention
Control measures must be specific to whether the infestation is indoors in a pantry or outdoors in a garden setting.
Pantry Control
For pantry pests, the first step is to dispose of all contaminated dry goods, sealing them in a plastic bag before placing them in an outdoor trash receptacle. Following this, thorough cleaning is necessary.
- Vacuum all shelves, cracks, and crevices to remove any hidden eggs or larvae.
- Wipe surfaces with a mild detergent or vinegar solution.
- Long-term prevention relies on proper storage, meaning new purchases of grains, flour, and cereals must be transferred into airtight containers made of glass or hard plastic.
- To ensure no hidden larvae survive, newly purchased dry goods can be frozen for at least four days, which effectively kills any weevil eggs.
Garden Control
For garden pests like the Black Vine Weevil, control often involves applying beneficial nematodes to the soil in the late summer or early fall. These microscopic organisms naturally hunt and kill the root-feeding larvae. Adults can also be managed by handpicking them at night when they are most active or by using sticky barriers on plant trunks to prevent them from climbing up to feed on foliage.