Flour Beetles

Flour beetles are tiny reddish-brown beetles that live in stored food such as flour, cereal and pasta. They belong to the genus Tribolium, part of the huge darkling beetle family, and they are among the most common pantry pests in the world.

Flour beetle Quick Facts

Common name	Flour beetle
Scientific name	Tribolium
Kingdom	Animalia
Phylum	Arthropoda
Class	Insecta
Order	Coleoptera
Family	Tenebrionidae
Type	Insect (darkling beetle)
Diet	Flour, cereals, pasta, dried fruit, nuts and other stored foods
Habitat	Pantries, mills, warehouses and grain stores
Native range	Red flour beetle probably Indo-Australian; now worldwide
Size	About 3-4 mm (1/8 inch)
Lifespan	Often a year or more as an adult
Colours	Shiny reddish brown

Because they are small, breed quickly and are easy to keep, flour beetles are also favorite animals for scientists. The red flour beetle was one of the first beetles to have its full set of genes (its genome) read.

Kinds of Flour Beetles and Their Relatives

There are several kinds of flour beetles. Their close cousins, the mealworm beetles, live in the same kinds of places and are often mentioned alongside them:

• Red flour beetle (Tribolium castaneum)
• Confused flour beetle (Tribolium confusum)
• Large or dark flour beetle (Tribolium destructor)
• Yellow mealworm beetle (Tenebrio molitor) – a related darkling beetle
• Dark mealworm beetle (Tenebrio obscurus) – another related darkling beetle

What Flour Beetles Look Like

Adult flour beetles are only about 3 to 4 mm long (around 1/8 of an inch). They are flat, shiny and reddish brown, with tough wing covers. Their larvae are slender, wormlike grubs that are white to pale yellow with two tiny pointed spines at the tail end.

Flour beetles do not bite or sting, and they do not spread disease. The problem is what they do to food. As they feed they leave behind shed skins, droppings and dead bodies, and they release smelly chemicals called quinones. Badly infested flour can turn grayish, smell sharp and taste bitter, and it can grow mold. Eating heavily infested food may upset some people or trigger allergies, so it should be thrown away.

Red Flour Beetle (Tribolium castaneum)

Red Flour Beetle

The red flour beetle is probably the most important pest of stored flour and grain products worldwide. It is thought to have come from the Indo-Australian region, but it now lives almost everywhere people store food. It does best in warm places and is especially common in warmer climates.

Red flour beetles eat flour, cereal, cake mixes, pasta, crackers, dried fruit, nuts, beans, spices and even chocolate. They are “secondary pests”: they struggle to break into whole, undamaged grains, so they usually feed on broken kernels, grain dust and milled products. They do not damage furniture, clothes or the house itself.

Adults can fly short distances in warm weather. They also live a surprisingly long time for such a small insect. Many survive for a year or more, and some have lived around three years in the lab.

Confused Flour Beetle (Tribolium confusum)

Flour Beetle – Photo by: Sarefo

The confused flour beetle got its name because people kept confusing it with the red flour beetle. The two look almost the same: both are small, flat and reddish brown.

The easiest way to tell them apart is to look at the antennae with a magnifying glass. In the red flour beetle, the last three segments are suddenly much bigger, forming a clear club. In the confused flour beetle, the antennae get thicker gradually toward the tip, with a club of about four segments. The confused flour beetle also rarely flies, while the red flour beetle can.

Confused flour beetles turn up in homes, grocery stores, mills, warehouses and silos. They hide in cracks in cupboards and pantry shelves, then crawl into open packages of flour, rice, cereal, beans and nuts.

Dark Flour Beetle (Tribolium destructor)

Flour Beetle – Photo by: Sarefo

The dark or large flour beetle is a bigger, darker relative, about 5 to 6 mm long and dark brown to nearly black. It is more often found in cooler regions, including parts of Europe. Like its cousins, it feeds on flour and other milled grain products, and it will also eat animal feeds and rolled oats.

Mealworm Beetle (Tenebrio molitor)

Flour Beetle – Photo by: Didier Descouens

Mealworm beetles are larger darkling beetles. The adult is a dark brown to black beetle about 1.2 to 1.8 cm long. Its larva is the famous mealworm, a shiny yellow-brown grub that grows to about 2.5 cm. Despite the name, a mealworm is not a worm at all.

Like all beetles, the mealworm beetle goes through complete metamorphosis: egg, larva, pupa and adult. A female can lay hundreds of tiny eggs. The larvae hatch in one to three weeks and molt many times (often 10 to 20) as they grow. The pupa is pale and does not eat, and within a few weeks it becomes an adult beetle.

Mealworms can be pests of stored grain and bran, but people also raise them on purpose. They are sold as food for pet reptiles, birds, fish and amphibians, used as fishing bait and put out in bird feeders. In some countries people eat them too, because they are rich in protein. The species probably came from Europe or the Mediterranean region but has spread around the world with people.

Dark Mealworm Beetle (Tenebrio obscurus)

Dark mealworm beetle – Photo by: NobbiP

The dark mealworm beetle is a close relative of the yellow mealworm beetle. Its larvae are darker and look very similar to ordinary mealworms. They are sometimes raised as feeder insects for pets, though the “mini mealworms” sold in pet shops are often a different beetle, the lesser mealworm. After several molts, the larva pupates and becomes a small, dull black beetle.

Amazing Flour Beetle Facts

• Flour beetles can survive in very dry food because they get most of the water they need from what they eat.
• They can survive doses of radiation far higher than would harm a person.
• In warm conditions, a flour beetle can go from egg to adult in about a month, so one female can start a big infestation quickly.
• Scientists use red flour beetles to study genes, behavior, evolution and how pests become resistant to insecticides.

How to Keep Flour Beetles Out of Your Kitchen

You do not need sprays to deal with flour beetles. The key is removing their food and hiding places:

• Check flour, cereal, pasta, pet food and spices for live beetles, larvae or a gritty, webby or bad-smelling texture. Throw away anything infested, sealed in a bag.
• Store dry foods in airtight glass, metal or thick plastic containers with tight lids.
• Vacuum shelves and cracks, then wipe them clean. Empty the vacuum outside.
• Freezing new flour or grain for several days kills any hidden eggs or larvae.
• Buy dry foods in amounts you will use within a few months, and use older packages first.

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Flour beetle FAQs