Weevils: What to Know

Medically Reviewed by Zilpah Sheikh, MD on January 24, 2024
7 min read

Weevils are small beetles with long, narrow snouts -- a characteristic of insects belonging to the Curculionidae family. Many species of weevil are agricultural and household pests. They're found on crops, plants, or in stored cereal grains.

When it's hot and dry, they take shelter in a building, slipping through the cracks. Although destructive, these pests don't poison the food they eat. However, they can infest all the grain in an elevator or bin if the conditions are right.

What do weevils look like?

These small bugs are about 0.125-0.25 inches or 3-6 millimeters long. They're shaped like tiny pears or light bulbs. They have long and slender snouts in front of their heads, six legs, and folded antennae. Some weevils have wings, while others don’t.

They're usually colored reddish-brown to black, and some have patterns on their wings. These insects have hard-shelled bodies with tiny holes or pits. They're commonly found in gardens and fields.

What do weevils eat? 

Weevils feed on crops and the roots of plants. They grow in cereal grains such as corn, wheat, oats, rye, buckwheat, and rice. They also feed on legumes (such as beans and peas), nuts, and cotton. They can infest grapes, apples, and pears.

A weevil’s life cycle

A weevil’s life cycle includes the egg, larva, pupa, and adult stages. Female weevils lay their eggs inside grain kernels or on plants. They lay small, white eggs in clusters. The eggs hatch into weevil larvae, which feed on the grain. Larvae look like small, white, or yellowish worms.

A larva grows inside the grain kernel and matures into a pupa. It forms a cocoon and changes (undergoes metamorphosis). Within a month, the weevil eats through the seed coat and emerges as an adult. Adults have a hard covering or exoskeleton and wings. The adults mate and lay eggs to begin the cycle again.

The lifespan of a weevil can vary based on environmental factors such as temperature and availability of food. Some weevils may live for a few months. But on average, their lifespan lasts a year.

There are many weevil species, including rice weevils, maize weevils, granary weevils, and root weevils.

Rice weevils

Rice weevils infest stored grains. They're reddish-brown and have four reddish or yellowish markings on the covers of their wings. Adult rice weevils can fly and are attracted to light. One female rice weevil can lay 300 to 400 eggs. She'll chew a hole in a grain kernel, deposit one egg there, and seal the hole with a fluid.

Maize weevils

These are similar in appearance to rice weevils and at one time were thought to be the same species. Maize weevils are 1/8th inch larger than rice weevils, and their grain of choice is corn, though they also eat rice and wheat.

Granary weevils

These resemble rice weevils and infest stored grains and grain products. They can be longer than rice weevils and are reddish-brown to black. Unlike rice weevils, they don’t have markings, can’t fly, and aren't attracted to light. A female will lay 50 to 200 eggs in the same manner as the rice weevil.

Root weevils

They grow on the roots of plants. Adult root weevils chew the leaves of shrubs, leaving distinctive notches in the leaves. The larvae feed on plant roots which may damage them. Root weevil species include the strawberry root weevil, black vine weevil, and lilac root weevil.

Weevils in flour

People may refer to the tiny insects sometimes found in bags of flour as "weevils," but they're more likely to be flour beetles. True weevils are rarely found in flour. As for the other insect, a female flour beetle will lay her eggs in food or food packages. These eggs hatch into worm-like larvae that you may see in your flour. Flour beetles only eat finely milled grains such as flour and meal. Rest assured, you're unlikely to get sick if you eat flour with a few "weevils" in it.

Boll weevils

Boll weevils are tiny beetles that eat cotton and can destroy cotton crops. They’re usually reddish- or grayish-brown, but the coloration may vary. The female lays her eggs within the bolls, flower buds, seed pods, or squares of developing cotton plants. When the eggs hatch, the larvae or grubs eat the fruiting structures, making them either fall off or ruin the cotton fibers.

Native to Mexico, boll weevils first showed up in Texas in 1892. It’s unknown how they traveled north, as these beetles don’t fly very far. However, they spread quickly. A single pair can make 2 million offspring in one season. Within their first 5 years in the U.S., boll weevils had caused a 50% decline in cotton production.

Federal and state governments, together with cotton foundations and associations, poured millions of dollars into researching boll weevil eradication. The first breakthrough was the discovery of boll weevil pheromones, which were used to lure and trap the pests. Scientists also found out that boll weevil development and reproduction slowed during low temperatures. By applying insecticide multiple times at short intervals, they found they could reduce and limit the ability of boll weevils to survive through the winter.

Thanks to cooperation between farmers, government officials, and scientists, boll weevils have been largely defeated.

Weevils are found worldwide. They're commonly seen in gardens and fields. They often crawl into your house through openings or cracks in doors, windows, or the foundation. They enter buildings to look for shelter in hot and dry weather conditions. They live in warm and moist places. You may see them in sinks, water basins, or bathtubs.

They also feed on grains such as rice, so you might bring them into your home if you buy grains infested with weevils.

You can easily spot a weevil infestation. If you notice a decrease in the weight and quality of stored grains, they’re probably infested by weevils. This is because weevil larvae and adults feed on grain.

Infested grain may have a white, sawdust-like appearance due to weevil droppings. Grain and grain products damaged by weevils have holes in them. It’s where the adult weevils emerge from.

Weevils are attracted to warm, moist environments. They emerge in late spring and seek shelter in the hot, dry months of June and July, looking for places to reproduce and lay their eggs. If they enter your home, they get attracted to grain and other food and infest them. If you get weevil-infested food, heating it to room temperature can promote the rapid growth of weevils.

Are weevils harmful?

Weevils are not harmful to humans, pets, houses, furniture, or clothing and don’t carry any diseases. They are temporary nuisance pests that damage stored food products. If weevils infest a garden or field, they can damage plants and reduce crop yields. Otherwise, they're harmless and go away on their own.

Do weevils bite?

Weevils don’t bite or sting you. They only feed on plants and food materials.

Here are some ways to get rid of weevils:

Root weevils

You can control root weevils with insecticide sprays such as bifenthrin, cyfluthrin, cyhalothrin, or permethrin. Spray on the base or lower part of plants. This stops the weevils from climbing up and damaging crops or plants. Spray the insecticide later in the day just before weevils become active. You can also spray permethrin around your house's foundations.

Weevil larvae grow in soil in the summer months. You can add beneficial heterorhabditis nematodes or roundworms to control the growth of weevils. Water the soil in the treated area to keep it moist.

Rice and granary weevils

Throw out any infested grain. Keep the uninfested food in sealed, airtight containers made of metal, glass, or heavy plastic to prevent infestation. Don't store in plastic bags, as weevils can chew through those. You can also store the food in the refrigerator or freezer to keep it fresh.

Extreme temperatures can stop the growth of weevils in all stages of their life cycle. You can freeze uninfested or slightly infested grain at 0 F for 3 days to prevent weevil growth. Or, place the grain in a shallow pan and put it in an oven heated to 140 F for 15-30 minutes. Either way, you'll have to pick the weevils out once they're dead.

If you have a weevil infestation in your kitchen, empty the shelves and vacuum them clean, especially in the cupboard corners and crevices. (Cleaning with detergent, bleach, or disinfectant won't keep these bugs away.) Household pesticides are not very effective against weevils and shouldn't be sprayed around food.

If you have a large infestation of weevils, opt for professional pest control and fumigation.

You don't need to spray your home with pesticides to keep weevils out. Here's what you should do instead:

  • Caulk any cracks or holes through which weevils may enter your home. 
  • Block areas under doors or windows.
  • Place shallow pans of water around the foundations or walls to trap weevils. Some, such as strawberry root weevils, are attracted to water.
  • Seal foods in glass, metal, or heavy plastic containers in your fridge until you're sure the weevils are gone.