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.

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

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:

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:

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:

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:

• The mealworms will molt 9-20 times before reaching their final size
• Molting is regulated by a hormone called juvenile hormone

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:

• Iron, potassium, copper, sodium, selenium, and zinc
• They can be compared to other food sources, such as beef and wheat bran

Here’s a comparison table of their nutritional components:

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.