Darkling beetles belong to the large insect family Tenebrionidae, encompassing over 20,000 species globally. These beetles, whose larval stage is the familiar mealworm, are generally scavengers. They are not known to bite humans and pose no significant threat.
Why Darkling Beetles Do Not Bite
Darkling beetles possess mandibles, which are chewing mouthparts common to many beetle species. These mandibles are structured for breaking down their primary food sources, such as decaying plant matter, fungi, and organic debris. They are designed for grinding and chewing, not for piercing human skin.
The physical structure of these mouthparts lacks the force or sharpness needed to break human skin. If a beetle explores a human finger, the sensation is a harmless exploratory nibble, not a true bite. Any reported instance of a bite is extremely rare and inconsequential.
How Darkling Beetles Defend Themselves
Since biting is not a viable defense, darkling beetles rely on physical and chemical deterrents. Many species, such as Eleodes (pinacate or stink beetles), possess specialized abdominal glands. When threatened, these glands secrete a foul-smelling chemical cocktail, primarily composed of benzoquinones.
This chemical defense is highly effective because the quinones are intensely irritating and distasteful to predators. The release of this spray is often preceded by the “head-standing” posture. The beetle raises its abdomen high, presenting the tip toward the threat as a clear warning before deploying the secretion.
Another common defense is thanatosis, or playing dead, where the beetle becomes motionless and rigid when disturbed. This strategy causes predators to lose interest, as they often prefer live prey. Because synthesizing defensive chemicals is metabolically costly, the beetle usually attempts posturing or playing dead before resorting to a spray.
Safe Handling and Common Encounters
The public most often encounters darkling beetles through their larval stage, the mealworm. Mealworms are widely sold as pet food for reptiles, birds, and fish, and are sometimes raised in homes. Other encounters occur when the beetles become minor pests, feeding on stored grains, flour, or dried pet food in pantries or barns.
If a darkling beetle needs to be moved, safe handling involves avoiding actions that could trigger its defensive spray. The best practice is to gently scoop the beetle onto paper or cardboard rather than picking it up directly. Squeezing or agitating the beetle with your fingers is likely to cause it to release its quinones, which can temporarily stain skin or clothing.