Warehouse Beetle

Warehouse Beetle scientific name: Trogoderma variabile Ballion

The Warehouse Beetle: An Introduction

Warehouse beetle is an accurate name for the insect. These pests are often found in warehouses that store food. Their love of food dictates their travels, which usually involves flying into warehouses to obtain it. These Northern Hemisphere insects can live for as many as 100 days, though their average lifespan is somewhere between nine and 50 days.

Warehouse Beetle

Warehouse Beetle

Warehouse Beetle Habitat and Food Source

Warehouse beetles aren’t known for dwelling in warehouses—just going in to obtain food. They have been found in homes and museums and are usually hiding out in dried grains and dried foods. They actually find home in grain products like seeds, candy, dried fruits, pet foods, nuts, and cereals.

Warehouse beetles apparently eat everything in sight, or what is in their natural environment. This includes animal-origin products like wool clothing, dead insects and animals, and dried milk. They also consume cereal, corn meal, candy, dog food, fishmeal, all kinds of seeds, flour, spaghetti, spices, peas, wheat, barley, and pollen. Is there anything they don’t eat? Why yes. They cannot eat whole grain; however, they can eat broken kernels of grain.

Life Cycle of Warehouse Beetles

The life cycle of the warehouse beetle—from egg to adult—is finished between 30 and 37 days. The female can leave more than a whopping 90 eggs in a food source. The eggs then hatch in approximately six days. The larvae begin crawling in the food and feeding. They are super active and move from one infested area to another, only to infest new sources of food. Interestingly, larvae prefer the dark and detest the light whereas adult females begin to be attracted to light after they finish laying eggs. Before pupation, the male has five molts and the female has six. During pupation, if natural crevices aren’t available, they will force their way through materials like wood and mortar. This stage takes around five days. In difficult living conditions, the adults eventually enter a resting state called facultative diapause, where metabolism tapers off and growth comes to a halt. The entire life cycle is finished in about six months.

Warehouse Beetles and Humans

Warehouse beetles are quite relentless. They have the ability to resist common control methods and starvation, making them quite the household pest. While they tend to be great food scavengers, warehouse beetles can actually survive up to a year without food during diapause. Larvae are usually easy to detect because of their coloring. They tend to hide out in food or in cracks in storage areas. In addition to their infestation, the many hair-like projections of the bugs are shed and can be an irritant to the respiratory and digestive tracts of anyone who is exposed to them. But, there is hope.

Warehouse Beetle Pest Control Methods

Control of warehouse beetles requires locating and eliminating infested objects, such as clothing and food items. Remember that it may be hard to find the source and that there may be more than one source. Follow these steps for removal of warehouse beetles:

  1. Carefully examine possible foods, and throw away those that are infested.
  2. Check easy-to-reach places where dead insects tend to collect.
  3. Fully vacuum clean cabinets and shelves to collect insects and spilled or infested items.
  4.  Note that washing shelves with disinfectants will not do any good to rid insect pests that are stored in products or containers. Insecticide sprays are also not recommended in areas with food; the sprays obviously have no effect on insects inside packages.
  5. If beetles are found in many areas of the house, you can use insecticides labeled “ant and roach killer” products. Lightly spray areas where insects are likely to dwell: cracks, corners, and edges.
  6. For severe infestation, a pest control operator should be contacted for professional treatment of the bugs.

Preventative measures include:

  1. Not putting exposed food on shelves. Instead, put food in containers with lids that fit tightly. Plastic bags are not a good idea.
  2. Cleaning shelves on a regular basis—particularly those where there is a chance of accumulation of flour or food particles. Good old soap and water will do the trick on flat surfaces. A vacuum with an attachment can clean out edges, cracks, and corners.
  3. Not mixing the old with the new. New food items can quickly be invaded if the old food has been infested.
  4. Never buying broken or damaged food packages—stay away! It is more likely that they will become infested.
  5. Maintaining dry storage units. Warehouse beetle pests are more likely to develop in moist environments.
  6. Eliminating nests in or around the home. Sometimes insects breed in rodent and insect nests and could travel into houses.
  7. Regularly checking and throwing away infested rodent baits, as pests can breed in them.

These creepy crawlers—and fliers—can be found in containers with dried food or inside wall spaces where food stuffs have accumulated or even where a dead rodent lay. One pest control operator noted that he located an infestation in a wall void where a pack rat had stashed a large amount of dog food! While a feisty household pest, there is hope for total elimination—if not by household methods, then by professionals.

Warehouse Beetles Entomology

The taxonomy of the warehouse beetle is as follows:
Kingdom: Animalia (animals)
Phylum: Arthropoda (arthropods)
Class: Insecta (insects)
Order: Coleoptera (beetles)
Superfamily: Bostrichoidea
Family: Dermestidae
Genus: Trogoderma
Species: Trogoderma variable (warehouse beetle)

Other members of genus Trogoderma include: Trogooderma anthrenoides, Trogoderma inclusum (larger cabinet beetle,) and Trogoderma ornatum.

Adult warehouse beetles are distinguished by these physical features:

  • Approximately 1/8 inches long
  • Oval shaped
  • Black or brownish-black in color
  • Three gray, golden, or reddish-brown lines across body
  • The wing covers (elytra) have brown and yellow patterns on a darker background
  • Wing covers have many hairs

Warehouse beetles in the immature stage are distinguished by the following characteristics:

  • Approximately ¼ inches long
  • Tan in color (yellow-white to reddish-brown)
  • Lots of hair

Detailed development and reproductive life cycle

The eggs of warehouse beetles are laid one at a time in processed commodity or in the crevices of whole kernels. The average length of this stage is about seven days. Normally, there are six larval instars; however, mature larvae can diapause. Molting can occur at intervals that are irregular. Diapause increases from 32% to 67% when at room temperature each day; this rises to 80% when handled or disturbed daily at room temperature. Diapausing larvae may put off pupation for as many as two years. It takes about 34 days to pupate if a larva does not diapause. Females generally pupate one more molt than males. Pupation typically occurs near food. The larval skin splits, and pupal development takes place within it, taking four days. Adults stay in the final larval skin for up to seven days and mate soon thereafter. Adult longevity maxes out at 100 days, occurring at about 12.8°C (55°F). A warehouse beetle’s life span ranges from nine days at 40°C (104°F) to 50 days at 17.5°C (63.5°F).