Learning To Grow Mealworms Pt. 2: The Mealworm Life Cycle

in Inner Blocks2 years ago

Mealworms are one of the most versatile organisms on the planet. Not only do they make a wonderful food source for many pets such as lizards, frogs, fish, and even chickens; but they can also be eaten by humans. Furthermore, it has recently been discovered that they have the ability to digest styrofoam without accumulating toxins in their tissues.

On a recent trip to Tractor Supply to pick up some chicken feed, I noticed big bags of dried mealworms stacked on a shelf right next to the feed. I considered picking some up as an extra little treat for our flock. That is, until I saw the price: 11 pounds for $69.99 USD! That’s $6.36 a pound!!

Now, I’ve been considering growing some mealworms on a small scale to use for fishing and little extra handouts for the chickens. But, after seeing how expensive they are, I am more than considering it. It’s time to do some research and make a plan.

Care to learn along with me?

Mealworm Life Cycle

As mentioned in a previous article, the mealworms that you feed to your pets or possibly eat yourself are the larval stage of an insect called the yellow mealworm beetle (Tenebrio molitor). And, like roughly 75% of all other insects, T. molitor undergoes a process called complete metamorphosis. This means that their life cycle consists of four distinct stages: egg, larva, pupa, and adult. “What about the other 25% of insects?”, you ask. Most (if not all) of them undergo incomplete metamorphosis. Most insects with an incomplete life cycle go through 3 stages: egg, nymph, and adult. The nymph that hatches out of the egg looks like a miniature copy of the adult, except it lacks wings, even if the adult form will eventually possess them. Interestingly, though, there are some insects like aphids that are viviparous. Instead of laying eggs, they give live birth to the nymph form of their life cycle.

I can feel myself being sucked down into a giant rabbit hole. So, before the topic of this writing gets changed entirely, I probably need to refocus: MEALWORM life cycle. Let’s start with the adult beetles.

Muséum de Toulouse, CC BY-SA 4.0, via Wikimedia Commons

Adult Beetles

Adult yellow mealworm beetles generally grow to a length of 1.25 - 1.8 centimeters. They are generally flightless due to their wings being fused to their body, making them easy to keep in captivity. While their name seems to imply that they are yellow in color, they actually start out brown and usually darken to black. The adult form of a mealworm beetle looks pretty similar to other ground beetles that you may find underneath the leaf litter in the forest, but there are a couple of features to look for if you are trying to them other ground beetles. The first place you’ll want to look is the abdomen. T. molitor will have evenly spaced linear grooves that extend down the entire abdomen Next, take a look at the hind legs. Mealworm beetles have four tarsal segments on their hind legs, whereas most other ground beetles possess five.

To tell the yellow mealworm beetle (T. molitor) from its close relative, the dark mealworm beetle (T. obscurus), you would want to compare their thorax and abdomen. T. molitor has a rectangular abdomen that rounds off at the end, and its thorax is as wide as its abdomen. T. obscurus has a rounder looking abdomen that comes to a point at the hind end, and the thorax is not as wide as its abdomen.

Beetles begin laying eggs somewhere between 9 and 20 days after emerging from their pupae. From there, they lay approximately 300 eggs over the remaining 2-3 months of their life cycle.


Mealworm eggs are tiny. According to some sources, they are about the size of a speck of dust or a grain of sand. Adult beetles will usually burrow into whatever substrate they are living in (dirt or leaf litter in the wild; oats or wheat bran in captivity) where they will lay a cluster of up to 40 eggs. The eggs are a bit sticky, so they tend to get covered and concealed by their substrate making it difficult for home growers to see them. Those hoping to cultivate multiple generations of mealworms must have a system for sifting their substrate and holding onto it long enough for any eggs to hatch. This can take anywhere from 1 to 4 weeks depending on temperature and humidity. Ideal conditions are somewhere in the range of 77-81 degrees Fahrenheit with about 70% humidity.

256pxTenebrio_molitor_larvae 1.jpg
Mnolf, CC BY-SA 3.0, via Wikimedia Commons


With the eggs being so tiny, it is pretty obvious that a newly hatched mealworm is going to be small. In fact, they can be separated from larger mealworms by sifting through a window screen. Frass, eggs, and newly hatched larva will pass straight through leaving older larvae in the sifter. After 4-6 weeks, they should be somewhere around a half an inch long. By the time they pupate (around 10 weeks after hatching), they may be as long as an inch and a half.

When larvae first hatch, they are white, soft-bodied little creatures. But over time, their exoskeleton begins to harden and turn translucent. This gives them the yellow color that the species is named for. However, as the mealworm eats and grows, that hardened exoskeleton remains static. Before long, the mealworm will have to molt or shed the old skin in order to continue growing. The stages of growth in between molts are called instars, and a mealworm will go through anywhere from 10 to 20 instars before becoming a pupa. So, if you’re serious about growing mealworms, you may have several thousand of them wriggling around in a tray. That’s a bunch of discarded exoskeletons that need to be separated! This must be another consideration for anyone raising these interesting little bugs.


Ivan.ch, CC BY-SA 3.0, via Wikimedia Commons


AJC1 from UK, CC BY-SA 2.0, via Wikimedia Commons


After about 10 weeks of squirming around as a larva, a mealworm enters the pupa stage. Within the protective shell of the pupa, the mealworm larva kind of liquifies before reforming into its final form.

The pupa starts off a creamy white color before eventually darkening to brown. During this stage of life, which usually lasts anywhere from 6-30 days depending on temperature and humidity, the insect is non mobile and does not eat. If the mealworm needs to overwinter, it can remain in its pupa form for up to 9 months. Once the adult beetle has fully formed, it will crawl out and leave its old shell behind, ready to mate and lay eggs for the next few months before dying.

In Conclusion

Mealworms have a longer life cycle than I expected. I didn't realize that they would stay in their larval form for up to 10 weeks. I also found it interesting how tiny the eggs and newly hatched larvae are, considering how large they grow to. However, armed with this knowledge, I feel more confident designing the setup I'll use to raise my own mealworms. Check back soon to see what I come up with.


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