You may have run across them invading your food cupboard. But what is a weevil? These bugs are commonly found invading the food products in your pantry. Although relatively harmless to humans, they do cause millions of dollars annually in food waste. The most common household varieties of weevils belong to the genus Sitophilus. There are about fourteen different species in this genus, and they originally come from the Himalayan Mountains. A weevil, according to the Oxford English Dictionary, is a small beetle with an elongated snout, that typically develop in the stems, seeds, and other parts of plants. They are common pests of crops and stored foodstuffs. 

Acorn Weevil
Acorn Weevil

Weevils generally are about 1/8-1/4” in length and are easily identified by their long snouts. Weevils get into food because the female digs a hole into the grain or seed and lays an egg there. As the larvae develop, they eat the meat inside until they reach adulthood and then crawl out. Weevils are not harmful to humans; however unsavory, they can be eaten along with the food they have invaded. Still, if you find dead weevils amongst your food items, there is the presence of pesticides that can be harmful to humans, and therefore, one should discard that food item. 

Weevils can chew through paper, plastic, and other thin food containers. To help deter weevils from getting into your pantry items, you should store flour, rice, grains, cereals, pasta, nuts, seeds, and other long-term items in tightly sealed plastic containers such as Tupperware.  Some weevils get into your home through cracks and other openings, but most come home from the grocer. Certain weevils, especially granary weevils, can come all the way from the farm. Weevils typically live for about eight months and can travel far from their origin. Common nuisance weevils often attack stored pantry items like rice, grain, flour, and cereals, among other items. The most common weevils found in homes are granary and rice weevils. One can also find occurrences of cigarette or drugstore weevils as well as the greater rice weevil, also known as the maize weevil.

Rice Weevils

Rice weevils are the smallest common house weevil and the most problematic. Rice weevils and granary weevils are similar in appearance. The rice weevil is only about 1/10in length and is reddish-brown to black with four distinct yellow, or sometimes red, dots on the forewings. The larvae are fat and cream-colored with a black head. The rice weevil has spread across the globe feeding on a variety of food products, including corn, dried beans, nuts, most grains, cereal products, and edible seeds (including birdseed). Some larvae have also been found in macaroni products as it closely resembles the development location of the larvae. 

Rice weevils reproduce quickly as females can lay up to four eggs per day. In temperate areas, the gestation period can be less than a month; in cooler temperatures, this can take much longer. Once the egg is laid, the larvae develop from pupa to adult within 18 days. However, the adults will stay for several more days inside the seed to harden and mature.  

Granary Weevils

The granary weevil, like the rice weevil, is reddish-brown. However, unlike its cousin, the granary weevil cannot fly. The rear wings of this bug are fused, creating a hard exoskeleton. Being roughly the same size as the food they infest, this provides a tough outer covering for the bug. Granary weevils are the only weevils that have not been found outside of human food-storage situations. The granary weevil is spread through trade, rather than flight and has invaded the world over. It can be found in dry pasta, corn, oats, rice, and other products. 

Granary weevils, like other weevils in the Sitophilus genus, have their roots in the Himalayan Mountains where they live off fruit trees. Because these pesky pests grow inside the seeds and kernels of food products, they were traded along with the grains that contained them. Humans did not know the grains were infested because you can’t see inside the kernels where the larvae live until maturity. These are also minuscule pests measuring only 1/10” in length. Unless you see the movement or spot darker spots in lighter colored foods, they are often difficult to detect. 

Why Do I Have Weevils?

The most common infestation method of weevils is through the supply chain. Granary weevils travel all the way from the silo to your home. With rapidly developing technology, weevils being transported from one location to another is less likely in modern times. In just one generation, the amount of complaints of pantry pests like the weevil has become significantly less frequent for pest control professionals. This is not a matter of the DIY generation, but rather advanced techniques for removing infested grains from the supply chain. Methods of detection and removal include centrifugal spinners that fling the bugs to their deaths, to x-rays infrared readers for detecting larvae inside the grains. Prevention and accidental transport have become much less frequent. Humans have become savvy at preventing these grain puncturing beetles from infesting their food stocks. 

Weevil Removal

To get rid of weevils, the most critical factor is identifying the source of the infestation. Once you have found the source, discard infested food items, and thoroughly wash the area affected. Use a vacuum to be sure to get rid of all larvae and adults and clean the area with soap and water. Do not use pesticides in areas where food is stored as this can contaminate replacement items, making them unsafe for human consumption. Avoid future infestations by keeping food items such as nuts, seeds, flours, and cereals inside plastic, glass, or metal containers with airtight lids. You can kill any infestations with high heat or freezing temperatures. Place infested items in the oven at a minimum of 120 degrees for an hour. Place in the freezer, at or below 32 degrees for one week or more. 

Resources

UF|IFAS Department of Entomology & Nematology
https://edis.ifas.ufl.edu/ig120
https://edis.ifas.ufl.edu/ig095

NPR
https://www.npr.org/sections/thesalt/2019/01/08/677763131/meet-the-granary-weevil-the-pantry-monster-of-our-own-creation

Science Direct
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/sitophilus

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Dusty Showers has been in the urban nuisance wildlife and pest control field since 1993. Taught by Garon Fyffe, a pioneer in humane nuisance wildlife management, Dusty has a passion for finding humane solutions to human & wildlife conflicts. Dusty was the only individual invited by the Florida Fish & Wildlife Commission in the lat 1990's to help write legislation for legal protection of Florida bats. With an instinct for solving wildlife, Dusty found pest control to be an easy "add-on interest". Dusty started his first business "Animal Instincts Wildlife & Pest Management" in the Tampa Bay, Florida area in 1995. Eventually selling Animal Instincts in 2002, Dusty went on to start Creepy Creatures Termite and Pest Control in 2009, which he still owns and operates today in Palm Harbor, Florida.

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