Insect of the Month

Warehouse Beetle (Trogoderma Variable)

This insect occurs in all life stages in warm buildings, throughout the year with two or three generations occurring each year. Females mate within one day of emerging from the pupa. Five to sixty eggs are deposited near a food site. Larvae will molt 5 or 6 times before pupating.

Both adults and larvae can feed on a wide variety of stored foods including cereals, candy, flour, fishmeal, noodles, dried spices, nuts, dead animal carcasses (drier stages), and pet foods. The larval stage prefers to hide in dark areas where food is stored, including processed and packaged foods, or in cracks and crevices where waste food has accumulated. The use of pheromone traps and inspections can determine the location and degree of infestation.

What do warehouse beetles look like?

Adults: Beetles are 2-3 mm (0.125 inches) long and brownish black in appearance. Their elytra (wing covers) are covered with fine hairs which can produce a mottled pattern in coloration.

Eggs: Oval, ivory in color and 0.5 mm (0.02 inches) long.

Larvae: 6-7 mm (0.25 inches) long and have a yellow white to dark brown colored body which is covered with tufts of setae (hairs) on each body segment. There are paired patches of concentrated setae on the last four abdominal segments and usually a tuft of longer hairs at the tip.

Pupae: Pupal cases are oval and hairy. Inside the pupal skin a whitish larva to blackish beetle may be visible.

What is the warehouse beetle life cycle?

The life cycle is completed in approximately 35 days. With poor food conditions, lower temps, or regular disturbance, the larval lifespan can be extended, and pupal stages may undergo diapause. Under these conditions, development can be extended by many months to over a year. Larvae rarely move from the site of egg laying if sufficient food is available.

Damage and Detection:

Both adults and larvae can feed on a wide variety of stored foods including cereals, candy, flour, fishmeal, noodles, dried spices, nuts, dead animal carcasses (drier stages), and pet foods. The larval stage prefers to hide in dark areas where food is stored, including processed and packaged foods, or in cracks and crevices where waste food has accumulated. The use of pheromone traps and inspections can determine the location and degree of infestation.

Fun Facts

Similar species include many other Anthrenus, Anthrenocerus, Attagenus and Trogoderma species.

Other common names include grain Trogoderma.

Warehouse beetle larvae have hairs on their body called setae that can cause gastrointestinal irritation in infants, children, and at-risk individuals. They may also cause an allergic reaction.

Warehouse beetles initiate flight at temperatures above 22.5°C (73°F).

The pheromone that attracts warehouse beetle also attracts similar species including:

  • Cigarette Beetle, (Lasioderma serricorne)
  • Confused Flour Beetle, (Tribolium confusum)
  • Saw-Toothed Grain Beetles, (Oryzaephilus surinamensis)

Recommended monitoring systems for the Warehouse beetle are: