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Quite a few of us have fed mealworms to our reptiles at various times, but most reptile collectors are entirely disconnected from the process. Mealworms are actually the larval form of the darkling beetle, and their life cycle is a process that shows off a lot of the awesome metamorphosis that can happen in more complex arthropods.
In the Beginning
Mealworms begin life as an egg of course. The darkling beetle that is the adult form of the meal worm typically burrows into softer soil and lays several hundred eggs. The egg is tiny, about the size of a grain of sand, and it takes a sharp eye to notice them even if you are raising your own mealworms. Once the egg is laid, they can take quite a bit of time to hatch. The average hatching time varies widely with temperature more than anything, although in most climes it will take from four to nineteen days.
Upon their emergence from the egg, the larval stage of the mealworm begins. Upon first hatching you’ll find that they are pretty much invisible to the unaided eye. Within a week or so of rapid molting however, the worms begin to take shape at a size that they can be clearly discerned. The newly hatched larva tend to be white, and the familiar brown color of the larger and more edible specimens occurs gradually.
During this stage of their life, these intrepid larva will devour nearly everything put in front of them. They primarily subsist on grains and small plants in the wild, although when being captive bred they’ll often be fed something high in protein like cat food to encourage a lot of growth.
From here they will begin their metamorphosis towards becoming a stately darkling beetle. The phases in an insect’s development as a larva in between molts are referred to as instars. Each time the mealworm sheds it’s exoskeleton it’s one step closer to becoming a pupa, and the worms typically go through between nine and twenty of these transformations before they get ready to become a pupa. The whole process, from hatching to becoming a pupa takes around ten weeks.
Growing Up the Worm Way
The pupa is a strange, white looking intermediate between the larval stage and the adult darkling beetle. This stage is mostly helpless, it can only wiggle slightly and has no real limbs to speak of yet. The mealworm will remain in this state for between six and twenty four days. In the wild this is a vulnerable state in which the soon-to-be-beetle might be eaten, but in captivity they’re virtually guaranteed to make it to adulthood.
The triumphant mealworm will eventually emerge as an adult darkling beetle, spreading forth into the world with some real mobility for the first time. They repeat the color cycle upon emerging, they’re light colored and soft shelled upon their entry to the world. Not so apparent to us, but readily apparent to them, they now have full sensory organs.
As the beetle ages they’ll gain the brown then black coloring that leaves them with the name of darkling beetles. Within four to twenty days of their emergence they’ll begin mating and laying eggs, thus entering the final stage of their life.
After the mating, the female beetle will delve into a soft substrate and begin to lay eggs. The darkling beetle is a prolific breeder, females will produce hundreds of eggs during the remainder of their life span. After a couple of months, the beetle has fulfilled its lifespan and will die of old age.
A Great Source of Nutrition
Mealworms are primarily raised for consumption by smaller animals. Many a reptile keeper has used them for this purpose, but others feed them to chickens, fish, and even predatory arthropods like scorpions. Their consumption is also becoming more and more common for people.
It might sound a bit icky, but the same nutritional benefits that make them an ideal animal feedstock also makes them great for human consumption. They’re high in protein, coming in second only to crickets as an insect source of protein. The larva are also quite high in calcium, like most insects, which can be a hard to find nutrient sometimes for those who avoid dairy. They do contain a bit more fat than crickets, so if you’re looking into adding them into your diet you’ll want to keep that in mind.
The darkling beetle is a commonly raised insect, they’re almost domesticated at this point. The larva make for an amazing food source for both pets and their owners, and their life cycle is a fascinating lesson in entomology. We hope that you’ve learned something about these fascinating insects, and that you just might find yourself with a whole new view of their secret world.