**Darkling Beetles** (family Tenebrionidae) are one of the largest families of beetles, named for their typically dark, dull black or brown coloration and their nocturnal habits. This family is extremely diverse, containing over 20,000 species. While most species are decomposers or beneficial components of forest ecosystems, some are significant **stored-product pests** (e.g., flour beetles, mealworms), and others, like the **Lesser Mealworm** (*Alphitobius diaperinus*), are major pests in poultry and livestock facilities.
Taxonomy and Classification
Darkling Beetles belong to the family Tenebrionidae in the order Coleoptera. They undergo complete metamorphosis. The famous **Mealworm** is the common name for the larva of the yellow mealworm beetle (*Tenebrio molitor*), a darkling beetle often reared as pet food. Many pest species are associated with dry, starchy materials, including grain, flour, dried goods, and animal feed.
Physical Description
Adult Darkling Beetles are usually dull black, brown, or dark gray, with a distinctive, hard, shell-like exoskeleton. They are generally slow-moving, and many species have elytra (wing covers) that are fused together, making them flightless. They range in size from tiny (2 mm) to over an inch long. They often have antennae that are thicker toward the tips.
The **larvae** are generally called **mealworms**—yellowish-brown, cylindrical, elongated, and hard-bodied, resembling wireworms but easily distinguished by their smooth, unsegmented appearance. The larvae of the Lesser Mealworm are common in poultry litter, where they feed on feces and decaying matter.
Distribution and Habitat
Darkling Beetles are found worldwide, particularly prevalent in arid and semi-arid regions. Their diverse habitats include deserts, forests (feeding on fungi and dead wood), and, concerning humans, grain storage facilities, feed mills, pantries, and chicken/hog houses, where they feed on spilled feed and organic waste.
Behavior and Life Cycle
The life cycle varies greatly by species and environment, often lasting a few months to a year. Females lay eggs in their food source or in nearby soil. Both larvae and adults are primarily nocturnal. Larvae feed continuously, with the long-lived mealworm stage being particularly damaging in stored products.
A key behavior of the Lesser Mealworm in poultry facilities is its tendency to bore into wooden structural materials and rigid foam insulation to pupate, which can cause significant damage to the building itself.
Feeding and Damage
Damage falls into two main categories:
- **Stored Product Contamination:** Species like flour beetles infest grain and flour, causing contamination with larval skins, frass, and body parts, making the product unusable and often introducing mold.
- **Poultry Facility Damage:** The Lesser Mealworm is an economic pest because its larvae bore into foam insulation and wood for pupation, causing structural damage. They also carry and transmit poultry diseases, including Salmonella and various viruses, necessitating rigorous management.
Management and Prevention
Management requires strict sanitation and source elimination.
- **Stored Products:** Thoroughly clean spilled feed and food. Store susceptible items in airtight containers. Freezing infested products for several days kills all life stages.
- **Poultry Houses:** A comprehensive program is needed: (1) **Sanitation**—removing old litter and waste, (2) **Structural Repair**—sealing foundation cracks and replacing damaged insulation, and (3) **Chemical Control**—targeted insecticide application to the foundation and soil beneath the poultry litter.
- **Exclusion:** Sealing off entry points in pantries and home storage areas is crucial.
Conservation and Research
While many wild species are beneficial decomposers, pest species are intensely studied. Research focuses on developing integrated pest management strategies for poultry facilities, especially focusing on effective, long-lasting chemical and non-chemical controls for the Lesser Mealworm that account for its ability to transmit pathogens.