Rice Weevil
The rice weevil is a tiny brown beetle with a long snout that lives in stored grain. It is one of the most common pantry pests in the world, and despite its name it attacks wheat, corn and many other grains as well as rice.
Rice weevil Quick Facts
| Common name | Rice weevil |
| Scientific name | Sitophilus oryzae |
| Kingdom | Animalia |
| Phylum | Arthropoda |
| Class | Insecta |
| Order | Coleoptera |
| Family | Dryophthoridae |
| Genus | Sitophilus |
| Type | Insect (weevil, a kind of beetle) |
| Diet | Whole grains such as rice, wheat and corn |
| Habitat | Stored grain, pantries, mills and warehouses |
| Native range | Probably South Asia; now worldwide |
| Size | 2.5-4 mm long |
| Lifespan | Adults usually live several months |
| Special feature | Larvae grow hidden inside a single grain |
What Does a Rice Weevil Look Like?
An adult rice weevil is only about 2.5 to 4 mm long, roughly the size of a grain of rice. It is dark reddish-brown to almost black, with four faint reddish or yellowish spots on its wing covers (elytra). Its body is covered in tiny pits, and its head stretches out into a long, thin snout with chewing mouthparts at the tip.
The rice weevil looks almost exactly like its close cousin, the maize weevil (Sitophilus zeamais). The two are so alike that scientists usually have to examine them under a microscope to tell them apart.
The larvae are small, white, legless grubs with a curved, C-shaped body. You almost never see them, because they spend their whole young life hidden inside a single grain.
Where Do Rice Weevils Live?
Rice weevils are found all over the world. They probably came from South Asia, but they have spread everywhere that people store and ship grain. They do best in warm, humid places, such as the tropics and subtropics. In cooler countries they survive indoors, in heated homes, warehouses, mills and grain stores.
What Do Rice Weevils Eat?
Both adults and larvae feed on whole grains and seeds. Besides rice, they eat wheat, corn (maize), barley, oats, rye and sorghum. They can also attack processed foods made from firm pieces of grain, such as dry pasta and some breakfast cereals.
The larvae need a solid kernel to grow inside, so they cannot develop in loose flour. Adults, however, will happily nibble on flour, crackers and other dry foods.
Life Cycle
Like all beetles, the rice weevil goes through four stages: egg, larva, pupa and adult.
- Egg: The female chews a tiny hole in a grain with her snout, lays one egg inside and seals the hole with a sticky plug. She usually lays just a few eggs a day, but can lay around 300 to 400 in her lifetime.
- Larva: The egg hatches after a few days. The grub eats the inside of the kernel, growing and molting several times while staying hidden.
- Pupa: When it is fully grown, the larva changes into a pupa, still inside the grain.
- Adult: The new adult chews its way out, leaving a small round exit hole and an empty, hollow kernel behind.
In warm conditions the whole cycle from egg to adult takes about a month. In cool weather it can take much longer. Adults usually live for several months, so a few weevils can turn into a large population quite quickly.
Behavior
Rice weevils are good fliers, which helps them spread from one food store to another. When they are disturbed, they often pull in their legs and play dead. They are attracted to warmth and moisture, and a bag of infested grain can even feel slightly warm and damp because of all the insects breathing and feeding inside.
Are Rice Weevils Harmful?
Rice weevils do not bite, sting or spread disease to people or pets. The real problem is the damage they do to food. They hollow out grains, leave droppings and shed skins behind, and make damp spots where mold can grow. Around the world, they cause major losses of stored grain every year.
How to Get Rid of Rice Weevils
The good news is that you can usually solve a rice weevil problem without any sprays:
- Find the source. Check every packet of rice, flour, pasta, cereal, popcorn, dried beans, bird seed and pet food. Look for live beetles and grains with small round holes.
- Throw out infested food. Seal it in a plastic bag and put it straight in an outdoor bin.
- Clean the shelves. Empty the cupboard and vacuum cracks and corners to remove spilled grain and hidden insects. Then wipe the shelves.
- Freeze or watch suspect food. Freezing a packet for about four days at around -18 C (0 F) kills all life stages. Or seal it in a clear bag or jar and check it for a few weeks to see if weevils appear.
- Store food in airtight containers. Glass jars or hard plastic boxes with tight lids keep weevils out and stop any you missed from spreading.
- Buy in smaller amounts. Use up older grain first, and keep stored food cool and dry.
If weevils keep coming back after a thorough clean-up, a pest control professional can help find hidden sources.
Rice weevil FAQs
Are rice weevils harmful to humans?
No. Rice weevils do not bite, sting or carry disease. They spoil food by hollowing out grains and leaving droppings, so infested food should be thrown away.
What happens if you accidentally eat a rice weevil?
Swallowing a weevil or its larva by accident is not dangerous. Cooking kills them, and they are not poisonous. It is still best to throw away heavily infested food because it may be moldy or stale.
Where do rice weevils come from?
They usually arrive in grain or packaged food that was already infested in a store or warehouse. Eggs and larvae hidden inside the grains are invisible, so the problem only shows when adults emerge.
Does freezing kill rice weevils?
Yes. Keeping infested or suspect food in a freezer at about -18 C (0 F) for around four days kills eggs, larvae, pupae and adults.
Can rice weevils fly?
Yes. Adult rice weevils fly well, which is one reason they can spread from one cupboard or food store to another.
Randi Jones is the owner and founder of the Nature Gift Store, an online retailer specializing in nature-themed gifts, educational science projects, live animal nature kits and real butterfly artwork. A biology graduate who fell in love with insects, she founded the company in 2001 to make active learning about nature fun, accessible and engaging for children and adults. Her store offers real butterfly frames, home and garden decor and educational live animal kits, including ant farms, worm farms, tadpoles, ladybugs and hermit crabs, and she runs a bug museum in Washington featuring live animals like Eddie the Iguana alongside other reptiles and insects.
