Weevils. Even the name can cause a shudder to anyone who has ever had these ugly, snout-nosed bugs in their flour, rice, or cornmeal. There are rice weevils, seed weevils, granary/grain weevils, maize weevils, and bean/pea/seed weevils. But the "true" weevils, with the snout nose, are the granary, rice, and maize weevils.
What Is a Weevil?
Often called flour bugs because that is where they are frequently found, weevils are a a type of beetle with an elongated snout. There are actually around 97,000 types of weevils.
How Weevils Get in Your Food
Similar to other pantry pests, granary and rice weevils will infest and feed on whole grains and rice as well as nuts, beans, cereals, seeds, corn, and other such foods.
But unlike beetles that live and feed on foods, these weevils actually live and feed inside the food. The female chews a hole into a seed or grain kernel and deposits an egg inside, then seals up the opening, leaving the egg behind. When the egg hatches (inside the grain/seed), the larva feeds on the meat inside until it is fully grown.
Once fully grown, the adult weevil eats its way out of the grain/seed.
Because the females emit pheromones, male weevils will be waiting outside the hole for her to emerge, and will immediately seek to bond with her to reproduce.
Weevils are 1/8- to 1/4-inch long, and are most easily distinguished by their long snouts. They can live up to 8 months and may venture far from the food originally infested.
Very tiny, this weevil is only about 1/16-inch long. The adult is dull reddish-brown to black, with four reddish-yellow spots on its back. The larvae are soft, white grubs with no legs. Pupae are similar to adults with long snouts, but they are white.
The adult rice weevil can fly, and lives up to five months, with the female laying up to 400 eggs during her lifetime.
Of the species of weevils that can fly, one of the most prolific is the red palm weevil. These weevils sometimes fly more than half a mile a day in search of locations for feeding and mating.
Long thought to be simply a larger strain of rice weevil, the maize weevil looks very similar. It is slightly larger, up to 1/8-inch long, and like the rice weevil, it is dull reddish brown to black with four red-yellow spots on its back. However, its coloring is generally darker than that of the rice weevil.
The rate of development is slightly slower for the maize weevil than for the rice weevil. Maize weevil larvae are soft, white grubs with no legs. Pupae, too, are similar to adults with long snouts, but they are white. And like the rice weevil, the maize weevil can fly.
The granary weevil is more cylindrical than the rice or maize weevil and is about 1/5-inch long.
Its coloring is similar to the rice and maize weevils: reddish brown to black. At about 1/4 its body length, the granary weevil's long snout extends down from its head. Its larvae (soft, white grubs without legs) and white pupae are similar to those of the rice and maize weevil.
This weevil cannot fly, so will be found close to the areas it infests. The adults can live up to 8 weeks, during which time the female can lay up to 200 eggs.
Stored Food Pest Damage
Partly because of its long life and partly because of its ability to fly, the rice weevil is considered to be the most destructive, but all three weevils can cause extensive damage to stored foods. When they infest grain that is stored in bins and remains undisturbed, they can completely destroy the food.
In the home, weevils can be brought in on packaged foods or they can come in from outside. Once inside, a population can grow and expand to food items stored nearby if the pests are not controlled.
Store grains and other weevil-tempting foods in dry areas, and always throw out any food where you find weevils. Clear any cupboards where you've found weevils and clean thoroughly before storing food there again, using a vacuum to be sure you've gotten all larvae.
You should avoid using chemical treatments to get rid of weevils because most are not safe to use around food.
Mutis, Ana et al. Evidence of Contact Pheromone Use In Mating Behavior of the Raspberry Weevil (Coleoptera: Curculionidae). Environmental Entomology, vol 38, no. 1, 2009, pp. 192-197. Oxford University Press (OUP). .doi:10.1603/022.038.0124
"Pantry Pests: Insects Found In Stored Food". University Of Minnesota Extension, 2019, https://extension.umn.edu/product-and-houseplant-pests/pantry-pests-insects-found-stored-food.
Weevils on Stored Grain. Pennsylvania State Extension College of Agricultural Sciences, 2017.