Rice weevils range in size from 1/8 inch to 3/16 inch (3.1 to 4.8 mm) and are dark reddish-brown in colour. The thoracic pits of a rice weevil are round or irregular in shape. Rice weevils often have four lightcoloured patches on its elytra (wing covers), but these are not always present or visible.
Rice weevils mainly attack whole grains such as wheat, corn, barley and rice, however they have been found actively breeding in such foods as macaroni and spaghetti when those materials are old and have become caked. They also have been reported to feed on beans, nuts, cereals, and have been observed sucking the juice from apples and pears. In homes, infestations are generally found in bird seed, nuts, decorative Indian corn and in rare instances, in old pasta stored in cupboards. The adults feed basically on the same foods as the larvae but not as restricted in their diets because the larvae need to develop inside whole grains. Rice weevils have well developed wings and are strong fliers. Flight also helps rice weevils infest grains stored at far ends of warehouses. Most infestation, however originated from nearby sources on infested grain.
Biology and life cycle
The rice weevil prefers warmer climates and so is more prevalent in the southern states. These weevils “play dead” when disturbed by drawing their legs close to the body and then lying still for several minutes. Rice weevils are internal feeders which means the larva develops inside whole grain kernels. Mating often occurs within 24 hours of adult emergence from grain kernels. Using her long, slender mouthparts, the female rice weevil bores a small hole into a grain kernel and then lays an egg in the hole. After sealing the hole with a gelatinous material, she proceeds to the next kernel to repeat the process. Over her life span of four to five months, the female will lay from 300 to 400 eggs, although as a general rule about 50 % of the eggs do not hatch. The egg hatches into a short, stout “C” shaped larva that is creamy white and has no legs. The larva feeds by chewing away at the inside of the grain kernel and will eventually hollow out the inside of the kernel. In warm conditions, the period from egg to pupa can last as few as 26 days but usually takes longer. After pupation, the adult beetle remains inside the kernel maturing and hardening. The adult then chews its way out leaving a small round hole in the grain. These open, round holes are a sign of a weevil infestation and are distinguished from the exit holes of the angoumois grain moth which leaves a little, hinged “lid” over the hole. Rice weevils are prolific breeders and can build up huge populations in stored grain to the point where the grain has little value as a food product. Literally tons of rice weevils have been screened out of heavily infested grain.