Rice Weevils, the Uninvited Pantry Pest
- HYUN SIM
- Apr 28
- 2 min read
If you store grains or grain-based products in a warm, dry pantry, you may eventually find small holes. This phenomenon is often the work of the Rice Weevil (Sitophilus Orzae). Their name comes from their tendency to feed and spend their entire lifecycle in grains, literally inside the grains. They are quite small, measuring around 2-4mm. Their bodies are dark colored being deep brown or nearly black. The elytra sports spots in a cross pattern. Their colors allow them to blend into the grains they infest (Aptive). Their prothorax is textured with deep punctures. Under the elytra are wings that only adults have. They are strong fliers and are attracted to light. If you refer to the image, you may notice their funny-looking snout. That is the rostrum. It is around 1/3 the length of the body and serves a very important function.
The rostrum has strong mandibles at the end that allow the Rice Weevil to drill into the hard shells of grains. This is necessary for breeding and feeding. The females will use their rostrum to drill and create a space large enough for a single egg to be laid. Do not be fooled, however; a female can lay up to 300 eggs in its lifetime - a large number, despite being one at a time. The female will then cover up the hole to decrease the likelihood of detection.
The eggs hatch after three days into a creamy white blob with a brownish-black head, devoid of legs (UME).
The larvae will eat the grain it is laid in from the inside. The feeding process takes around 18 days until all that is left of the kernel or grain is the thin seed cover (InsectLimited). They then enter a pupal stage that lasts around 4 days until the fully matured adult emerges (InsectLimited). The larvae cause the most damage to the seeds as their presence causes mold and bacteria (FLApest). The hollowed-out seeds eaten by the larvae feel lighter and can easily be crushed to dust.
The adults can fly but they have some common traits with other insect species. They are attracted to light and only fly at temperatures above 20 degrees Celsius (68 degrees Fahrenheit) (InsectsLimited).
They are found worldwide but seem to be more prominent in the Southern United States (FLApest). Despite their name, they infest many other foods. Their targets include corn, wheat, rice, beans, nuts, cereals, rye, buckwheat, stored cotton, wheat products, grapes, apples, and pears (UME).
When it comes to infestation areas, they are attracted to warm and dry places that contain little security. Improperly sealed or unsealed packages provide ideal conditions for a Rice Weevil infestation (FLApest). When the infestation is on the heavier side, the sound of chewing can be heard (InsectLimited).
If you find them snacking and they sense you, they may play dead by drawing their legs in close to their body (FLApest). They are common and considered a pest by many. People counter them using traps with pheromones that attract the males. The Rice Weevil will show up without an invitation and feed on the grains left unsealed and unprotected, living up to their reputation and name.
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