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Warehouse Beetles

General Facts

One of the most common stored-product insect pests in the world, the warehouse beetle can wreak havoc in pantries when left unchecked. The insects are found across Canada and affect various commodities, including legumes, nuts, animal feed, barley, wheat, pollen, and stored seeds. Despite their preference for stored products, the pests are not overly particular about what they eat and have also been known to feed on animal skins, fur, hair, pet food, and dead insects as well as other animal carcasses. Warehouse beetle larvae inflict the most damage on pantry items, as adults are short-lived and rarely feed on stored food products.

Appearance / Identification

top view of warehouse beetle
Adult warehouse beetles appear oval in shape and range in length from 3 to 5 mm. Their outer wings, the elytra, are hair-covered and generally dark in colour, with bands that vary from brown to red. The body colour is typically darker brown or black, though some warehouse beetles may appear mottled. Larvae are yellowish-white but grow darker as they mature. The larvae of the warehouse beetle can grow up to 6 mm in length and are distinguishable by the tufts of hairs that line the body.

See more pictures of warehouse beetles.

Habitat

Found throughout Canada from New Brunswick to British Columbia, the warehouse beetle thrives in temperate environments and can be found anywhere from large-scale grain production facilities to home pantries. The pests are commonly found in flour and feed mills, warehouses, dried milk factories, stored-grain facilities and distribution centres, and processing plants. Warehouse beetles have even been known to infest the nests of bees, rodents, and birds.

Diet

Adult warehouse beetles maintain a diet that focuses more on nectars and pollens, though they have also been known to feed on dead insects and the dried carcasses of other animals. Larvae, on the other hand, feed on a variety of common foods and pantry items, including cereals, seeds, cornmeal, dried pet food, spices, pasta noodles, cookies, candy, and milk powder. Sometimes, infestations start when the pests feed on insect or animal carcasses found in warehouses and distribution centres before moving on to the products that are manufactured or stored there.

Life Cycle / Reproduction

Females lay around 90 eggs in a lifetime, and the resulting offspring go through a life cycle that takes anywhere from two to four months to complete. In cases of food shortages or poor environmental conditions, warehouse beetle larvae can slow their development by molting numerous times before deciding to pupate. This extends the larval stage of the life cycle and helps ensure the survival of developing warehouse beetles, and thus the success of the species. In fact, warehouse beetle larvae have been known to remain in diapause, or suspended development, for over a year in unfavourable conditions. Pupation occurs directly on a food source to allow the emerging adults to mate immediately. Adults live anywhere from a few days to a few months, depending on the temperature of the environment.

Problems Caused by Warehouse Beetles

The warehouse beetle creates various problems in the stored food industry especially. As larvae can chew through most protective wrappings, including plastics and aluminum foil, pantry items remain susceptible to infestation when not monitored. Furthermore, the setae, or shape hairs, on the body of the larvae can cause gastro-intestinal irritation in infants, children, and susceptible individuals that result in vomiting and diarrhea. For extremely sensitive individuals, the hairs may also cause an allergic reaction.

Detection / Signs of Infestation

The most common sign of a warehouse beetle infestation is the presence of the molted skins that the larvae cast off as they pass through the various larval instars and before pupating. A sighting of several adult warehouse beetles is indicative of an infestation, though the extent of the problem may vary. Finding larvae in stored food proves the presence of the invading insects, as well.

Prevention Tips

Carefully monitor and inspect all possible food sources regularly, especially items stored in containers that are easily breached. Thoroughly vacuum cabinets, shelving, and hard-to-reach places where insects tend to collect. Rotate products to use stored foods with earlier expiration dates first, and try not to mix older foods with newer ones. Additionally, store pantry items in glass jars with securely fastened lids instead of bags, plastic containers, or any other storage device made from a less durable material.

Control / Removal

Pheromone traps and appropriately labelled insecticides may be used to control minor infestations, but always read and follow the directions on the label. For larger infestations of warehouse beetles, contacting a pest management professional may prove beneficial or even necessary. Trained in the safe and proper use of insecticides and other management methods, pest management professionals can eliminate warehouse beetle infestations.

Pictures of warehouse beetles.