Build your mealworm knowledge-base.
Mealworms have risen to fame in the last five years or so as one of the most popular edible insect species.
If you are here, you either have tried them or are thinking of doing so.
But you feel you need to know more about them.
Great!
You've come to the right place.
Let's start a mealworm quick tour.
1. Mealworms are NOT worms
Let's say you have given in to the temptation of raising mealworms at home.
You have bought some of those little yellow wrigglers from a pet shop.
Then, you put them all snug in a container (like for example a plastic box) in your room.
You give your mealworms a nice substrate to burrow in, and you gave them cereals and vegetables to feed on.
One morning you wake up, walk to your mealworm microfarm to see how your pets are doing and....
... the container is all crawling with BEETLES!
This is a classical scenario that will await a beginner in mealworm breeding who has not done his/her homework, to get to know the peculiarities of the mealworm biology and life cycle, because...
... mealworms are not worms!
They do look wormish, but these nice little bugs are actually... beetles!
So, what are mealworms?
Mealworms are the larvae of darkling beetles.
Darkling beetle is one of the names that the adult insect is known by.
"Darkling" because of its colour once the mealworm has finished turning into an adult beetle: it will go from white to brown to black.
2. Mealworms have legs. And a skeleton
If you have taken a closer look at your mealworms, you will have noticed another revealing detail... they have LEGS!
Short and not very visible, but legs, alright.
Six of them.
All sprouting from the thorax, right below the head.
Worms, on the other hands, have no legs.
Remember, mealworms are larvae.
Very different from the adult insect that they will turn into.
So the body of the mealworm is quite different from that of the darkling beetle.
Much of it will change.
The legs though will stay.
They will grow quite a bit.
In the larval stage they are not designed so much for walking but for burrowing. So they are short.
The adult darkling beetles, in contrast, are fast runners.
Try exposing them to the light and you’ll see!
Mealworm anatomy
The legs are attached to the three segments of the thorax (proto-, meso- and meta – thorax).
The thorax is one of the body parts of the mealworm, the others are the head and the long abdomen, made of nine segments. The last segment is pointed and called "spine".
The abdomen is where the mealworm stores all the fat produced by the large quantities of food it eats.
It will need the fat later, in the pupa phase, to support the transformation into an adult beetle.
This accounts for the high content in fat (nearly, 30%).
The Exoskeleton
Mealworms have another thing that worms do not: an exoskeleton.
That means a skeleton wrapped AROUND the body, instead than a skeleton INSIDE the body.
The shape is different, obviously: no bones, but a semi-rigid envelope.
Made not of calcium but of chitin.
Why is this so important?
Chitin is an amazing fibre that can provide you with a series of health benefits.
3. Mealworms have four lives: meet the amazing Mr. Tenebrio
The meal "worm" is one of the four life phases of the darkling beetle. Scientific name: Tenebrio Molitor.
We can loosely translate it as "the dark miller", because it loves to chew grains.
The "worm" is the larval phase in the mealworm life cycle.
The life cycle of the mealworm develops across four stages: egg, larva, pupa, imago (adult insect)
In its larval phase, after hatching from an egg and before turning into a pupa, Mr. Tenebrio does in fact resemble a worm.
And it loves to feed on meal (ground cereals, aka flour) if it can get inside a pantry.
That's how it got its popular name.
Mr. Tenebrio is a holometabolous insect.
Oh gosh!
What the hell does this mean?
This exotic (* Greek, from: from hol- + metabolos = changeable) definition means that Tenebrio Molitor undergoes a complete metamorphosis... cycling through the four stages we already mentioned.
It also means that the larva is very different from the adult.
All beetles have the same four-stage life cycle, and so do butterflies and moths, flies, and wasps.
While crickets and grasshoppers undergo an incomplete metamorphosis of only three stages — egg, nymph and adult.
4. Mealworms are originally pests from Africa
Where do mealworms come from?
There is an interesting little fact here.
You might not know this, but mealworms migrated from Africa.
Later, they got naturalized in North America. And Europe as well.
How did this little bug manage to come so far?
Very likely, hidden in some shipment of grains, that got infested by mealworms (hence their name).
Humans have been familiar with mealworms for millenia.
An archeologic study reports evidence of mealworms in a famous prehistoric site in today's Turkey: the legendary city of Troy!
You may be curious...
Where can mealworms be found in nature?
In nature, mealworms love to lay low under rocks or to colonize pieces of rotting wood (darkness, moisture and warmth are what it seeks...).
Darkling beetles like to feed on decaying organic matter.
Like vegetables and rotten leaves, but also animal matter and seeds.
At a certain point though, the history of Tenebrio Molitor got mingled with humans.
And the darkling beetle discovered that the human environment can be so much more plentiful.
Especially in places where improperly stored grains and flours get damp... A real feast for always hungry mealworms!
So Mr. Tenebrio Molitor added to its career the role of pest... it can infest grocery stores, cereal warehouses, and chicken coops too.
It can even damage infrastructure, munching on materials more resistant than food like.... styrofoam!
It's not a joke, but we will tell you the full story about this later.
Remember this when you plan a mealworm farm: take care to organize your containers in a way to prevent escapes.
Not so difficult, but give it a thought.
A couple of runaway beetles probably will not change your life, but you never know when they can decide to start a family (or.... a dynasty!) in your kitchen cupboard or in your garden.
A female mealworm beetle can lay as many as 500 eggs...
Kinda like this:
That makes for a laaaarge family of critters!
5. Mealworms LOVE darkness. From birth.
Mr. Tenebrio likes darkness, as its name says (* tenebra means "darkness" in Latin).
So in nature it would start its life there, in darkness, as a nearly invisible tiny whitish egg... Like a grain of rice but smaller.
Its mama would bury hundreds of them in the ground were they could also have the warmth that is necessary for the eggs to hatch.
Remember this if you want to organize a mealworm farm:
You'll have to recreate similar conditions to get more generations of healthy mealworms.
Mama Tenebrio, when she can raise her family in human surroundings, loves to bury her mealworm eggs in flour.
So the babies can start eating straight away as soon as they hatch.
If you go into mealworm breeding, provide a similar environment and it will be a full success.
Give them a layer of substrate thick enough for them to burrow in: at least 2-3 inches (5-8cm).
If you use some edible material, like cereals, you will solve part of the feed too, in one move.
Adding some egg cartons to help Mr. Tenebrio hide from the light will make it happy.
In nature, it would hide under rocks or behind tree bark, or dig itself in the ground or some heap of rotting leaves.
6. Mealworm eggs hatch faster in damper environments
How long does it take for mealworm eggs to hatch anyway?
In normal conditions, one or two weeks.
BUT keep in mind that your mealworms are VERY sensitive to temperature and humidity.
If the conditions you provide for them are NOT optimal, the life cycle of Mr. Tenebrio could turn into a much much longer story.
Keep those eggs in a nice warm environment, but without overdoing it... something around 77 F (25 C) will do.
They would prefer a relative humidity in the range of 50-60%,.
So if you live somewhere with a dry climate add a high-sided bowl of water to the mealworm container.
The same goes for the larval-worm phase, the one that is most interesting to us.
Why?
You will find out in the next chapter.
But let's get back to our hatched eggs.
Baby mealworms are out... but you will hardly notice at first sight!
They are very, very small
Your best chance at spotting them without a magnifying glass is noticing some movement in the substrate.
There, they will be happily wriggling and searching for food.
Eating and growing is what mealworms are all about.
So keep those babies immersed in some edible substrate and they will very soon become more than visible!
7. The mealworm life cycle is faster with higher temperature and humidity
Your first batch of larvae will take usually 8 to 10 weeks to mutate into pupas, depending on a series of factors.
Temperature, humidity and what you feed them are the most relevant.
Keep in mind this: if you start your mealworm herd from larvae bought at a store, they will probably have different ages.
As a consequence, some will pupate sooner and some later.
Usually, experimenting with mealworms starts from the larvae.
It will take you a couple of generations of mealworms to getting it right.
From familiarizing with the complete mealworm life cycle to establishing a controlled routine.
So two months in the larval phase can become four if you get something wrong.
Especially if you don't keep your little herd warm and moist enough.
Remember... African origins!
So, nothing below 70 F (21 C), and better in the 77/80 F range (let's say 25/26 C for you Europeans out there).
Humidity: in nature Mr. Tenebrio would prefer damp hideouts, like rotting leaves or wood, or crawl under a rock.
If you are keeping your mealworm farm in a closed space, check that it does not get too dry.
And if necessary choose a bowl with tall sides, fill it with water and place it in the container(s) as an air humidifier.
8. You can keep your mealworms alive in the fridge.
Mealworms will not freeze to death below the temperatures suggested above.
But they will grow sort of lazy...
Take-your-time style.
By the way, if for some reason you need to slow down the life cycle of mealworms (going on holiday, for example?), you can... put them in the fridge.
Mealworms can hold out to temperatures lower than -10 C¨, surprisingly enough for a bug of African origin.
But they have a little survival secret to cope with cold weather, as scientists the University of Utah and the University of California found out: they called it "antifreeze proteins" or AFP.
AFPs prevent ice crystals from growing by binding to them when they are very small.
This explains some cases that have been reported of mealworms miraculously "resurrecting". After they have been taken out of the freezer.
Sort of like Jesus.
9. Mr. Tenebrio sheds its exoskeleton as a snake does with its skin
We have already mentioned the exoskeleton, that protects the soft parts of the mealworm.
There is one peculiarity about the exoskeleton: since it is rigid, it cannot grow... but the mealworm does!
So Mr. Tenebrio has to shed its exoskeleton several times to be able to grow to its full size (usually about an inch or little more, e.g. about 2,5 to 3 cm.).
A little like a serpent changing its skin.
When it comes to insects, this procedure is called "molting" and it also affects colour.
Our little friend will be all white and soft after discarding its previous exoskeleton, while the new one still has to harden... then it will gradually darken to yellow and light brown,
A mealworm will molt from 8 to 20 times during its larval phase.
You should harvest the mealworms during this period of their life cycle.
Which lasts on average a couple of months.
If you wait too long, they will pupate.
10. A mealworm pupa has no mouth. And no...
The day comes when you start to find some new "presences" among your mealworms: whitish, slightly curled in a C-shape and mostly motionless.
Your mealworms have started turning into pupae.
Mr Tenebrio, after eating so much and growing to a respectable size, now has to spend some twenty days as a pupa.
Done with eating!
Eating and growing was for the larval phase: the pupa has no mouth!
Ahem... the pupa has no anus either (no pooping).
Its job is: transformation, aka metamorphosis.
In other words, the pupa is busy preparing all the body parts of the future beetle.
While doing this, it does not eat or poop and it barely moves at all.
Keep an eye on your pupas and learn to spot the signs when one is ready for the Big Transformation.
Watching a new darkling beetle emerge from its wrapping is a fascinating experience.
A mealworm turning into a beetle is really amazing!
The other reason to keep an eye on them is very practical.
The newly emerged beetles will snack on their pupa colleagues which are still there, motionless and defenseless.
So it is a good idea to remove beetles and relocate them to a separate container.
The pupa has been working hard to grow those stumps of legs into six proper insect legs.
And the two wing buttons into full elytra (the hard sheaths on the back that can open) and wings.
The new beetle pushes from the inside to get rid of the pupa envelope and finally sheds it.
Surprise!
When it first emerges the darkling beetle is actually.... white!
In just a few hours it darkens into a brown hue and then finally into black.
The darkling beetle is now center stage in full splendour.
11. A female mealworm beetle can lay hundreds of eggs... and other beetles eat them!
In a couple of weeks our darkling beetle will find a mate and start a family.
After their honey moon, Ms. Tenebrio will provide hundreds of offsprings laying some 300 to 500 miniscule eggs.
The eggs will hatch in a couple more weeks.
And a new mealworm life cycle will begin.
One word of caution for the beginner mealworm breeder...
Adult beetles will eat both eggs and baby mealworms!
I'm glad that humans aren't doing this... 😃
There are several farming techniques out there, with solutions to separate the voracious adults from the eggs and larvae.
Find one that suits you, do a bit of experimenting and settle for the one that fits best in your farming routine.
But don't forget about this detail.
Even the larvae (the mealworms) can have a mind to snack on eggs.
The fact is that mealworms are scavengers.
In nature they would eat decaying organic matter. This includes dead leaves and dead insects or animals.
You can keep mealworms on a vegetarian diet of cereals plus some bits of carrots, potatoes, apples, for moisture.
But keep them well fed or they will turn to cannibalism.
Also keep in mind that... we are what we eat, and the same goes for mealworms!
If you want them to be a food rich of nutrients, don't be stingy with their menu.
12. Nutritional values of mealworms can vary a lot.
If you have already done a bit of research on the nutritional values of mealworms, you have probably noticed that the numbers given by different studies and reports are by all means NOT the same.
They can show a very ample range between minimum and maximum.
Take for example the two main nutritional factors: proteins and fats.
You will find for proteins values that can go from 38% to 55% (depending on the report), and from 27% to 33% for fats.
These are not small differences!
Why is that so?
Well... go back to what we have seen so far: humidity, temperature and diet have a great influence on the life of the worms.
It is such a little fellow that small variations have big consequences.
Then again, there are different techniques of handling mealworms before slaughtering them.
If you raise them for feed, a technique called "gut loading" is often used.
Giving them plenty of food, more than usual and richer, to make them accumulate more nutrients.
Breeders of mealworms for human consumption may want to let them fast for a day or two to let them empty their bowels...
Let the waste go into frass (fertilizer), not onto your plate!
Again, we are talking of a small bug, so these maneuvers are likely to impact its content of nutrients.
The amount of fiber doesn’t changing
Not surprisingly, the values for fibre do not show large differences.
You will find them quoted somewhere between 7% and 10%.
The exoskeleton is the main factor for fibre (chitin), and it will stay the same.
Here you have some findings from a recent study (August 2018) on the nutritional values of mealworms.
One important detail.
Mealworms have a high content of fatty acids, in particular Omega 3 and Omega 6
This is particularly important because our bodies need Omega 3 and Omega 6.
They are essential.
Meaning, our bodies can't produce them, so we need to get them from food.
Omega 3 fats are part of cells membranes.
They are necessary for the production of hormones that regulate blood, heart, and genetic function.
Omega 3 can be useful in preventing heart disease and stroke.
It may help control lupus, eczema, and rheumatoid arthritis, and may protect against cancer.
Omega 6 are beneficial to brain function, muscle growth, and hormone production.
Caution!
They are also inflammatory and competing with Omega 3.
So, you should take them in small quantities.
In the nearest future, we are going to see many more studies on mealworms and the human diet.
They are just getting into the eating habits of Europe and North America.
And, the literature is still scarce.
In the meanwhile, use common sense and don't eat mealworms by the tons....
13. Mealworms are easy to breed
The number one advantage of mealworms, from the point of view of a micro farmer, is that they are easy to breed.
Probably the easiest among edible insects.
For example.
A comparison with the super-popular crickets
Mealworms do not stink (like crickets).
They are silent.
Their possibility of escaping from a smooth-walled container are practically zero.
All this means that you can easily do some micro-farming experiment even in your room.
With the data from the previous paragraph in mind, you have a simple knowledge base to know your way around mealworms.
Now you know who (what) they are and what to expect.
You know what mealworms like (a warm, damp and dark living space, plenty to eat, above all cereals).
Some more hints.
You don’t need to provide drinking water, some vegetable bits in the food will be enough for that.
Though you can add also leafy vegetables and/or bits of fruit, this task requires monitoring.
You need to check whether the feed has been completely eaten, and remove the remains often, to avoid rotting.
And also...
Avoid Mold
While it is true that mealworms love decaying organic matter, if forgotten bits of feed develop molds, you could run into problems.
Molds are almost never good for health, not even of insects.
So, keep it simple: use drier and firmer vegetables.
Carrots are the best, according to most mealworm breeders.
They stay fresh and firm for a long time and are full of vitamins.
It goes without saying, that if you DO get mold in your microfarm substrate, you have to remove it and sanitize the container well.
Go by your nose: mealworms do not produce foul smells by themselves.
So if something smells rotten – you have a problem
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We will not go into the details of mealworm farm design this time...
For now, it is enough to suggest that you plan some solution to separate eggs + larvae from pupae and adults.
As we saw before, beetles can be cannibals and feast on their young (eggs and very small baby worms).
If you're planning on playing with a few mealworms, you can use three separate containers.
Remove pupas, and later adult beetles, by hand to place them in their "section".
This will become time-consuming if numbers grow large, obviously.
Stay tuned for more useful mealworm knowledge, if you are thinking seriously about becoming a microfarmer. There is more to come!
14. Mealworms can eat Styrofoam and not die!
This is NOT a joke.
Mealworms do eat styrofoam.
Not only do they eat it, but they do so in perfect happiness and health, as reported by researchers of the Universities of Stanford, California, and Peking, China ("Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 1. Chemical and Physical Characterization and Isotopic Tests").
"Styrofoam" is a popular name for a product, made by extrusion, of polystyrene (PS). A synthetic aromatic hydrocarbon polymer made from the monomer styrene.
Polystyrene was generally thought to be non-biodegradble... although some micro-organism known as Methanogenes can degrade it very slowly.
But you cannot breed mealworms for eating!
The numbers are quite impressive.
About 100 mealworms could consume between 34 and 39 milligrams per day of polystirene.
Keeping in mind the ease and speed of breeding of mealworms, polystyrene composting by these lovely bugs sounds quite possible.
What can really blow your mind are two facts:
- Mealworms fed ONLY polystyrene for a whole month turned out to be as happy and healthy as the ones fed a normal diet (bran).
- What goes into the mealworms is polyestyrene, what comes out is 49,2% useful frass (their poo which can be used as fertilizer) and 47,7% carbon dioxide, CO2
These were the results obtained by the Stanford scientists over a 16-day period.
We have to thank the bacteria leaving in our dear bugs' guts for this miracle! ("Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 2. Role of Gut Microorganisms" ).
Now that you know, you can have fun setting up a small styrofoam composter with part of your mealworms.
Just don't play the guinea pig testing whether this diet is good for humans too!
The scientist will probably find a way to test this too in the coming years...
