Tribolium 101: Identifying a Flour Beetle

• Tribolium castaneum – red flour beetle
• Tribolium confusum – confused flour beetle
• Tribolum destructor – destructive flour beetle
• Tenebrio molitor – mealworm beetle
• Tenebrio obscurus – mini mealworm

Each species possess distinctive physical (and biological) features, but all share common traits that groups them into the Tribolium genus.

Flour beetles are holometabolic meaning they undergo the complete metamorphosis life cycle from egg -> larva -> pupa -> adult.

The life span of an average adult flour beetle is approximately three years. A single adult female can lay up to 450 eggs in her lifetime at a rate of 2 to 3 eggs a day. Eggs will hatch into larvae into 5 to 12 days and become full-grown in about 30 days. The larval stage usually goes through 7 to 8 instars and grow to around 3/16 of an inch with a yellow tinge. Flour beetles are most voracious eaters during their larvae phase. Matured larva transform into cocooned pupa which is when flour beetles are most easily identified of their gender (we will see how to identify the sex of a flour beetle in a later post). From the pupa emerged the new adult beetle and the entire cycle from egg to adult takes around 6 weeks under optimal conditions.

Destructive (or dark) flour beetle pupa hatching to an adult

Let us first analyze the similarities and differences between the two most common flour beetle species: the red flour beetle and the confused flour beetle.

Red Flour Beetle (Tribolium castaneum) vs Confused Flour Beetle (Tribolium confusum)

Both species are nearly identical in physical composition. In fact, the “confused” flour beetle is named due to it being confused with the red flour beetle.

Both species are reddish-brown in color and about 1/8 of an inch in length. They leave in the same environments and compete for the same resources. The egg, larva, and pupa stages of both species are also very similar. The eggs are white, microscopic, and covered in sticky secretion with adheres flour bits. The larva phase has a creamy yellow color and two dark pointed projections at its posterior. The pupa is a lighter shade of yellow and looks similar to the Pokemon, Kakuna.

The defining differences between these two species is evident in their antenna. The antenna of the red flour beetle ends in a 3-segmented club and the sides of the thorax are slightly curved. The confused flour beetle has no apparent club on the 4-segmented antennae and the sides of the thorax are straighter. One additional distinction is that the red flour beetle may fly, especially before a storm, but the confused flour beetle does not fly.

Red flour beetle (left) and Confused flour beetle (right) | Purdue

Destructive flour beetle (Tribolium destructor), Mealworms (Tenebrio molitor), and Mini Mealworms (Tenebrio obscurus)

These three species are distinctive due to their dark-brown coloration.

The destructive flour beetle got its name due to the destructive damage it causes to stored grain products.

destructive or darkling flour beetle (Tribolium destructor)

Mealworms and its miniature sister species are high in protein content and makes them great food sources for reptile, fish, and bird pets.

Many cultures also consider mealworms to be delicacies and have even been incorporated into tequila-flavored novelty candies.

Tequila flavored mealworm (top) and mealworm-covered caramel apples (bottom)

References:

Rebecca Baldwin and Thomas R. Fasulo.  2003. “Confused Flour Beetle, Tribolium confusum and Red Flour Beetle, Tribolium castaneum”. Entomology and Nematology Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville.

Dennis Calvin. 2001. “Entomological Notes”. Department of Entomology, College of Agricultural Sciences, The Pennsylvania State University.