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Thriving Everywhere
If you look hard enough just about anywhere on the planet you are bound to find a Darkling Beetle. From fertile forests to arid deserts, Darkling Beetles have adapted and thrive in nearly every environment. Here we see a large specimen on the lookout for food.
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Take note of the thick, hard shell and plain appearance of this beetle. It's easy to overlook, especially when in the shadows and nooks and crannies where they like to hide.
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Tenebrionidae
It is estimated there are approximately 20,000 species in this large family of beetles. The family name literally means "seeker of dark places" so it's easy to see how the name Darkling Beetle came into common usage. Add to this their dark coloration and tendency toward nocturnal activity and the name becomes an even more obvious choice.
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Armor
Darkling Beetles are very rugged. Their thick exoskeleton helps to protect them from predators and the environment.
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Anatomy
Like all beetles their body is divided into 3 sections (head, thorax and abdomen) and they have 6 legs, 2 antennae, and compound eyes. Hidden beneath their armor are wings, though these are rarely used and in some species the outer wings are fused making them useless.
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Grubs
Here we see what appear to be worms eating a green apple, but those aren't worms. They're grubs, the immature form of the Darkling Beetles we see eating the red apple. Judging by appearance it would be difficult to tell these are different life stages of the same species.
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The only physical similarity is the 6 tiny legs just behind the grub's head. But the truth is each of these grubs will someday become a beetle.
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Larva
The grub is the larval stage of the Darkling Beetle's life. The large, heavily armored grubs are much longer than they will be as adult beetles. To help them survive they posses mandibles capable of delivering a painful bite, and their slick shell makes them difficult to grip.
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Omnivorous
Fulfilling the role of scavengers, Darkling Beetles and their grubs will feed on dead leaves, rotting wood, fungi, as well as decaying animal matter. As we see here, they also enjoy fresh and rotting fruits and vegetables. In fact, they will eat just about anything they can get a hold of.
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Feeders
Because they are easily bred and maintained in captivity the larval stage of Darkling Beetles are often used to feed pets. You can purchase mealworms (the larva of Tenebrio molitor) and superworms (the larva of Zophobas morio, the species we see here) at most pet stores.
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Mealworms
Mealworms get their name from their habit of invading and consuming stored grains, and for this reason are considered pests. But an ongoing study at Stanford University discovered they have the ability to consume and degrade polystyrene into usable organic matter, turning this pest into an ecological asset.
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Metamorphosis
But how does a grub become a beetle? Once the grub has grown to the proper size by accumulating enough food, it forms into a pupa. They are very vulnerable in this stage, barely able to move, so they first seek out a safe space hidden from danger.
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Here we have collected specimens to observe as they go through this fascinating process. From left to right, we have a pupa, 2 pupa in the process of breaking from their pupal casing, and finally a fresh adult Darkling Beetle.
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Metamorphosis
Darkling Beetles experience complete metamorphosis (holometaboly) in their lifetime. Beginning life as as egg, they hatch into their larval stage (nymph or grub), form into a pupa, then emerge as adults. An estimated 40%-60% of all life forms go through a similar 4-stage process of metamorphosis.
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Pupa
The exoskeleton of the grub is shed as the body of the pupa begins to assume the shape of the adult beetle. Meanwhile inside, complex changes are taking place. In a few weeks, using the resources collected as a grub, the adult form becomes complete.
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Casing
Shedding the pupal casing is a process very similar to molting. The pupa becomes very soft and pushes out the back of the casing. Once freed the beetle expands its new body to its adult size and shape.
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Adult
Once the pupal casing is shed, the adult beetle emerges. The new exoskeleton with be stark white until, over time, it hardens and darkens to the familiar black armor we expect to see on a Darkling Beetle.
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Chemical Attack
In addition to their hard armored shell Darkling Beetles have one more rather surprising defense. When provoked they release a chemical attack by spraying a foul-smelling liquid from special glands.
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We got a little too close to this Darkling Beetle and that white foam behind its eyes is sending us the message to back off. We can count ourselves luck. Some species spray these chemicals from glands in their back end.
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Quinones
The nasty smell is produced by organic compounds called quinones. Bombardier beetles also make use of quinones in their defenses. Within the realm of biology quinones and their derivatives are common, serving functions in respiration, blood coagulation, bone formation and other processes. Quinones also have industrial uses such as in the production of hydrogen peroxide, dyes and pigments.
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Stink
The smell is intended to dissuade predators from making a meal of the beetle. Since most predators make contact using their mouth or nose, getting this stinky substance delivered to such a strategic location can be enough to distract the predator as the beetle escapes.
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Reproduction
The adult Darkling Beetle's main objective is reproduction. After breeding, females lay their tiny eggs and the small grubs that hatch go to work collecting food in preparation of becoming the next generation of adults.