by LARPD Volunteer Docent Wally Wood

Walking in any outdoor park, I’m sure at one time or another you have met a darling Darkling beetle and exclaimed, “Look, a Stink Bug!” 

The name darkling means "lover of darkness"; the English language term 'darkling' means "characterized by darkness or obscurity". 

Darkling beetles (Family Tenebrionidae) are a diverse group of insects with more than 20,000 species worldwide. Known for their tough exoskeletons, flightless bodies, and nocturnal habits, these beetles thrive in a wide variety of habitats—from scorching deserts to lush woodlands! Many are scavengers who recycle organic matter, while some are pests of stored grains.  

What’s that Smell? 

Well, the black beetle you found ambling along is harmless. They are just out looking for a rotten log to chew on and probably not happy to see you. If they feel threatened, they will do a headstand and stick their rear end into the air to release a pungent odor (benzoquinones) smelling somewhat like kerosene.  This unpleasant odor is harmless to humans. While stink bugs do not bite, sting, or carry diseases, their secretions can be irritating. In rare cases, contact with their bodily fluids has caused keratitis (eye irritation) in humans: Do Stink Bugs Release Toxins. Their secretions can also irritate the skin or gastrointestinal tract of pets if ingested.  However, they are not considered toxic in the same way as venomous animals. 

Cycle of Life 

Throughout their lives, Darkling beetles undergo complete metamorphosis, consisting of four stages: egg, larva, pupa, and adult beetle. 

Egg Stage: Females lay eggs in dark, moist environments. Eggs usually hatch within 1-2 weeks.  

Larval Stage: Larva, commonly known as “mealworms”, is the longest and most variable phase, lasting from several months up to 18 months. Larvae molt multiple times as they grow.  

Pupal Stage: Pupae are immobile and do not feed, undergoing internal transformation into adults. This stage lasts 1–3 weeks, influenced by temperature. 

Adult darkling beetles emerge with a soft exoskeleton that hardens over a few days.  

The overall lifespan of darkling beetles is highly variable, ranging from a few months to several years, with most species living 1–3 years, though some species can survive up to 10 years.  Most of their life is spent in the larval stage, accumulating energy for metamorphosis.  

Egg-laying usually begins one to two weeks after the adult beetle emerges. The eggs are small, white, and bean-shaped, and they hatch within 4 to 19 days, depending on temperature and humidity. Eggs are typically laid in clusters of 50 to 100 at a time, often buried in soil, grain, or other organic substrates to provide food for the emerging larvae.  

Mealworms are commonly used as feed for pet reptiles, fish, birds and rodents. This gives a slightly sadistic meaning to the word “meal” – worm. In nature, they are an important part of the natural ecosystem, eating decaying matter and keeping things clean. 

Stink Bug for Dinner, Anyone? 

In their native habitat they do have a few enemies. Crows, coyotes, foxes, hawks, ravens, and snakes. Various small mammals actively hunt darkling beetles, which form part of their omnivorous diets. Rodents, such as mice and voles, and other small mammals like shrews and hedgehogs  frequently forage these beetle in their nocturnal activities. 

One type of mouse (Grasshopper Mouse), more common in the desert, has learned to grab a beetle and plant the beetle in the sand rear end first. Then proceed to dine on the front end of the beetle like it was an ice-cream cone without the fear of being sprayed. 

Close Encounters of the Darkling Kind

Darkling beetles are likely to be encountered in: 

• Open grassy areas near creeks or rivers  

• Open fields, parks, and along trails 

• Damp, sunny spots where decaying vegetation is present 

So the next time you wander through the park, if you encounter this harmless beetle, contemplate his amblings while enjoying this realm we share. 

Valley Wilds Newsletter October 2026