Mealworm Life Cycle: A Fascinating Journey from Larva to Beetle

Mealworms, often mistaken for worms, are in fact insects that belong to the darkling beetle family. They undergo a complete metamorphosis, including four life stages: egg, larva, pupa, and adult. The larval stage, commonly referred to as the mealworm, presents an excellent opportunity to study their life cycle.

These creatures thrive in moist, dark, and undisturbed environments, making them commonly found in stored products and plant materials. Studying mealworms can lead to a better understanding of their growth performance and nutrient composition, as they are increasingly considered a sustainable food source for humans due to their low environmental impact.

Throughout the mealworm’s life cycle, they exhibit various physical characteristics. For example, larvae darken in color as they grow and molt, shedding their skin multiple times before reaching the pupal stage. Subsequently, they transform into nocturnal, black, hard-shelled adult beetles. By observing these fascinating changes, one can appreciate the complexity and beauty of the mealworm’s metamorphosis.

Mealworm Life Cycle Overview

Eggs

  • Tiny, white, bean-shaped
  • Hatch in a few weeks

Mealworms begin their life cycle as tiny, white, bean-shaped eggs. After a few weeks, the eggs hatch, progressing to the next stage of their life cycle, the larvae.

Larvae

  • Also known as mealworms
  • Golden brown color
  • Shed skin multiple times

During the larval stage of their life cycle, mealworms have two main goals: eat and grow. As they grow, they continually shed their skin, transitioning from white to a shiny honey-yellow color, and darken slightly before molting again. Larvae can molt from 9 to 20 times before reaching the pupa stage.

Pupae

  • Transitional stage
  • Non-feeding

In the pupa stage, mealworms cease feeding and undergo transformation to become adult beetles. This stage is crucial for their metamorphosis. Like caterpillars and butterflies, mealworms go through a complete metamorphosis in three stages: larvae, pupa, and adult.

Adult Beetles

  • Nocturnal, black beetles
  • About one inch long
  • Lay eggs for the next generation

Once a mealworm has transformed into an adult beetle, it begins a new phase in its life cycle. These adult beetles are nocturnal, black, and hard-shelled, measuring approximately one inch long. Typically found in moist, dark, undisturbed places, these beetles play a vital role in laying eggs for the next generation of mealworms.

Habitat and Environmental Factors

Temperature and Humidity

Mealworms thrive in specific temperature and humidity levels. They prefer a temperature range between 20°C – 30°C (68°F – 86°F), as it allows for optimal growth and development. Maintaining a humidity level between 60% – 70% ensures a healthy environment for the insects. Higher humidity levels can lead to mold growth.

Natural Habitat

In the natural world, mealworms are commonly found in moist, dark, and undisturbed habitats. These include accumulations of:

  • Decaying leaves
  • Animal droppings
  • Wood shavings

Darkling beetles, the adult form of mealworms, are nocturnal insects, further emphasizing their preference for dark habitats.

Substrate

Mealworms require a proper substrate to support their growth and development. The substrate serves as both a food source and a place for the larvae to live. Ideal substrates for mealworms include:

  • Wheat bran
  • Oatmeal
  • Cornmeal

When supplemented with fresh plant materials, mealworms show improved growth performance and nutritional value.

Material Avg. Weight After 32 Days
Wheat bran 6.18 mg ± 1.34%
Wheat straw 2.54 mg ± 0.89%

In summary, mealworms require a controlled environment with proper temperature, humidity, natural habitat, and substrate to flourish.

Feeding and Nutrition

Natural Diet

Mealworms (Tenebrio molitor) primarily feed on decaying organic matter and grains. In the wild, their diet consists of:

  • Food: Dead insects
  • Vegetation: Decaying leaves, bran, grains

Captive Diet

In captivity, mealworms can be fed a varied diet to optimize their nutrition. Some suitable food sources include:

  • Bran: A common substrate for captive mealworms
  • Grains: Can be supplemented with oats, wheat, or rice
  • Fruits and vegetables: Apple, potato, and carrots for providing moisture
Natural Mealworm Diet Captive Mealworm Diet
Primary food source Organic matter, grains Bran, grains
Supplemental food source Dead insects Fruits, vegetables
Protein source Dead insects Grain, bran
Moisture source Decaying vegetation Fruits (apple, potato), water

It’s important to provide mealworms with a balanced diet to promote their growth and maintain their nutritional value. Overall, both diets play an essential role in the life cycle and development of mealworms.

Reproduction and Breeding

Mating Process

Darkling beetles, the adult form of mealworms, follow a simple mating process. The male locates a receptive female and engages in mating by mounting her. Mating may take place multiple times throughout their life cycle1.

Egg Laying and Hatching

Female darkling beetles lay hundreds of eggs in their lifetime, usually in dark and moist environments to ensure optimal conditions for the larvae to thrive. The eggs are tiny, white, and bean-shaped2. The incubation period ranges from 7 to 10 days1.

After hatching, the mealworm larvae undergo multiple stages of growth and development before transitioning into pupae, and eventually, adult beetles2.

Comparison of Life Stages:

Life Stage Characteristics
Egg White, bean-shaped, approximately 1/120 inches long2
Larva Cylindrical, yellow to golden brown, molts 9-20 times2
Pupa Transition stage between larva and adult, immobile
Adult Darkling beetle, black, hard-shelled, 1 inch long1

Common Uses

Pet Food

Mealworms are a popular food for many reptiles, birds, and small animals. They are:

  • Rich in protein
  • Easy to digest
  • A good source of energy

Examples of pets that enjoy mealworms include:

  • Bearded dragons
  • Geckos
  • Chickens
  • Hedgehogs

Human Food

Mealworms have become an increasingly popular ingredient in human food, especially in Asian countries. Insect-based dishes are known for their:

  • High protein content
  • Sustainability
  • Low environmental impact

Some examples of mealworm-based food items are:

  • Insect burgers
  • Mealworm pasta
  • Protein bars

Fishing Bait

Mealworms are commonly used as fishing bait for various types of fish, including:

  • Sunfish
  • Crappie
  • Trout

They make excellent bait because they:

  • Are easy to handle
  • Have a strong, natural scent
  • Can be stored for extended periods

Comparing mealworms to other types of fishing bait, such as earthworms or crickets:

Bait Type Accessibility Storage Duration Ability to Attract Fish
Mealworms Easy Long Moderate
Earthworms Moderate Short High
Crickets Moderate Moderate Moderate

Mealworms and Plastics

Consumption of Polystyrene

Mealworms have been observed to ingest different types of plastics, such as high-impact polystyrene (HIPS), expanded polystyrene (EPS), and low-density polyethylene (LDPE), but not linear low-density polyethylene (LLDPE) or polypropylene (PP) 1. The gut microbiome of mealworms contributes to the degradation of plastics like polystyrene.

Potential Environmental Benefits

The biodegradation of plastics by mealworms could offer a potential solution to the growing issue of plastic waste. It is, however, essential to recognize that mealworm-excreted HBCD (a common flame retardant) still poses a hazard, and that other common plastic additives may have different consequences within plastic-degrading mealworms.

Comparison of Plastics Consumed by Mealworms:

Plastic Type Consumption by Mealworms
HIPS (Polystyrene) Yes
EPS (Polystyrene) Yes
LDPE (Polyethylene) Yes
LLDPE (Polyethylene) No
PP (Polypropylene) No

Environmental Pros and Cons of Mealworms Degrading Plastics:

Pro:

  • Reduces plastic waste buildup
  • Offers an alternative for plastic disposal

Con:

  • Excreted HBCD still poses a hazard
  • Not all plastic additives are degraded efficiently

While mealworms could help with certain types of plastic waste, it’s crucial to remember the importance of developing biodegradable materials and reducing plastic usage as a more holistic approach to tackling the plastic waste crisis.

Additional Facts

Molting and Growth

Mealworms are the larvae of darkling beetles and go through a process called molting. They have four life stages: egg, larva, pupa, and adult. The larval stage is when they molt their exoskeleton multiple times:

Throughout the molting process, the larvae grow in size. Eventually, they transform into pupae where they remain motionless. Inside the pupae, the mealworms develop into beetles, completing their life cycle.

Nutritional Composition

Mealworms, specifically Tenebrio molitor, are considered a sustainable food source for humans and other animals. Their nutritional composition is rich, with a variety of minerals and other nutrients:

Here’s a comparison table of their nutritional components:

Nutrient Mealworms Beef Wheat Bran
Iron High High Low
Potassium High High Medium
Copper Medium Low Low
Sodium Low High Low
Selenium High High Low
Zinc High High Medium

Feeding mealworms a diet supplemented with fresh plant materials like carrots can improve their nutritional value. As prolific breeders, yellow mealworm beetles can be reared in various conditions, including environments with stored grains, where they may emit distinctive odors.

Footnotes

  1. Beetle Life Cycle | Ask A Biologist 2 3 4

  2. Rearing Mealworms | Digital Fact Sheets – U.OSU 2 3 4

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Mealworm Pupa

 

Strange cocoon
Location: Finland
January 25, 2011 5:15 pm
Hi there,
I found this strange bug cocoon underneath my fridge and am a bit worried that we’re about to be infested with an alien species. Can you tell me what it is?
Signature: Freaked Out

Mealworm Pupa

Dear Freaked Out,
This is a Beetle pupa, but we are uncertain of the species.

Hiya,
Thanks for replying so quickly. Once you wrote beetle I had a thought.. mealworms. I have baby newts here at the moment and was trying to feed them mealworms, and I reckon the cat got one and dragged it off and now it’s changing into it’s beetle state. Weird looking thing though isn’t it? Thanks for replying, much appreciated!
Thanks,
Lisa

Letter 2 – Advice on Raising Meal Worms requested

 

Mealworm confusion, looking for expert
Website: http://www.rabbitindustrycouncil.com
December 18, 2011 7:44 pm
I know you’re terrifically busy in all senses of the word ‘terrific’, but I was hoping you might ask your entomologist backup crew to get in touch.
I’m starting out with mealworms and have some rather odd things going on in the colonies.  Major size differences in larval stage just before pupation and in pupae is only the beginning…!
I’m suspecting a mix of species, but which species?  Need to know so I can give them each their optimum environments, and I’m totally lost. 🙂
Have pics, can send, can take more…
And any help, as always, is wonderfully appreciated!
Signature: Pamela Alley

Mealworm Pupae

Mealworm pupae size difference
Location: N. California
December 18, 2011 7:55 pm
You ROCK, folks…!
This is a picture of a darkling beetle, matured from one of my mealworm colony pupae–and in the next pictures, you can see there is a huge size difference between two distinct groups. Supplier A’s mealworms are larger at pupation and make large pupae; Supplier B’s mealworms are pupating at a smaller size and result in smaller pupae.
I suspect a mix of species–let me know what photos will be most helpful in ID’ing the darn things?
Thanks so very much for all you do–I swear, I recommend you to about six teachers a year. *evil grin*
Signature: onafixedincome

Mealworm Pupae

Ed. Note:  These two emails came minutes apart, and despite the different signatures and email addresses, we suspect they have the same origin.

Darkline Beetle: Mealworm

Dear Pamela and/or Onafixedincome,
Since your two emails came minutes apart, and deal with a similar subject matter, we suspect they are related despite different signatures and different email addresses.  Please confirm our suspicions.  Additionally, since only onafixedincome sent photos, we are treating this as a single posting and we will respond to both together.  Mealworms are a common commercial name for the larvae of Darkling Beetles that are raised as food for a variety of pets including larger tropical fish, turtles, lizards and frogs.  The Aquatic Community website has a nice page on Raising Mealworms.  The common commercial species is the Yellow Mealworm,
Tenebrio molitor, though we suspect other species may also be raised commercially, which might be one explanation for the size discrepancy you have witnessed.  Individual species also have considerable variation in size from individual to individual, and this may be partially explained by genetic traits.  Perhaps one supplier has individuals that are passing on a gene that is producing smaller larvae and pupae, and this is producing smaller adults.  We hope someone with experience will provide a comment to this posting, though sometimes comments take years to be posted.  We would recommend that you place a comment to this posting so that you will be notified in the future if there are any comments or answers to your questions.

Whups!  My apologies, wasn’t trying to be sneaky…Just brainless as usual, which takes little effort. 🙁
I wasn’t going to send you pics, because they are ‘domestic’ insects, then thought you might find them fun, if not useful, so posted them.  The difference in emails was a screwup, and I am sorry.
Any rate, I appreciate your input as always!–can’t imagine how you manage to keep up with all this stuff.
Given the current average of malformation (50%+) thus far on the large pupae, I’m leaning toward the theory that these were treated with with growth hormone to get size–and that the beetles from these may well turn out sterile. 🙁
So, I guess I’ll just have to wait and see….Much obliged for the link, it’s always good to learn as much as you can when raising anything, even bugs! 🙂
Again, you ROCK!!!
And of course, thank you so very much. 🙂
PA
onafixedincome

Authors

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  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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5 thoughts on “Mealworm Life Cycle: A Fascinating Journey from Larva to Beetle”

  1. Well, I’ve had these guys for about a year now. Learning a lot! Did track down the original supplier of the ‘super size’ mealies, and yes, they had been treated and were sterile. The chickens adored them, at least. 🙂

    They really took off come warmer weather and I froze a LOT for winter supplementation of chicken diet–yay!–but oddest of all, I found that sitting and ‘working’ the mealies is something of a meditative time.

    HOWEVER: HEALTH CAUTION!!
    Apparently, developed allergies to mealworms and their bedding is quite common, so it is HIGHLY RECOMMENDED that one wear a mask when working in/around the bins, and not recommended to keep them in close proximity to living areas (Or you can set up negative air pressure cabinets, that works. LOL!)

    Thanks again for your support and knowledge!

    PA

    Reply
  2. Thank you so much for posting this. I have been really freaked out as well when I found these things in my leopard gecko habitat. I too thought they looked like aliens! It freaked me out and made me sick to my stomach just having to touch it.

    Reply

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