Does the Mealworm get a Turn?
by Jim Greenwald

When one starts to feed large cichlids one turns to worms and as the worm turns the turns usually end up going towards meal worms. For those who have never tried meal worms they are a great food for all carnivorous fish. I have fed them to Arawanas, Oscars, Dempseys and many other fish with big mouths.

If you keep fish that are carnivores and insectivores that require live food, you should raise at least one feeder insect to give to your fish from time to time.

Lets talk about mealworms, I have kept two different types but the one that is most readily available is the larva of darkling beetles, Tenebrio molitor. Everyone who has ever kept reptiles or amphibians that require live food has probably fed them mealworms. The mealworm (Tenebrio molitor) is accepted by the widest variety of carnivores and insectivores, and is also the easiest to keep. Mealworms are odorless, clean, can handle widely varied temperatures, and require minimal space and attention.

The larva of Tenebrio molitor is the mealworm most commonly used as reptile and amphibian food and the one I will discuss here, but you can also find two larger mealworms available. Tenebrio grows to about one inch, and is a golden yellow in color (white if just molted). Abnormally large Tenebrio larvae are sometimes available commercially. These larvae are fed a juvenile hormone that prevents the mealworms from pupating. Instead, the larvae simply keep growing (up to 1 1/2 inches). Eventually, a few of these giant mealworms manage to pupate, but most die during the larval stage. These "giant mealworms are not to be confused with Zoophorba moriom which grows up to two inches in length and is available commercially under the names "super mealworms" or "giant mealworm." Zoophobias have a dark head, tail and a band on each body segment.

Understanding how to raise mealworms is understanding their Life cycle

Mealworms are the larvae of darkling beetles. Darkling beetles undergo complete metamorphosis, and have an egg, larva, pupa and beetle stage. There is normally one life cycle per year, although it can vary from 4 months to 2 years. The female lays 500 to 1000 bean-shaped, white eggs.

These are seldom seen because they are sticky and rapidly become coated with flour. Eggs hatch in about a week, although it may take a few weeks before the larvae have grown enough to be readily seen. A larva molts several times as it grows, and can reach full size in as little as three months, although this is extremely variable and may easily take as long as seven months.
A pupa, without a protective case, eventually forms, and this stage lasts for about two weeks, the pupa has the ability to move via a snapping motion throughout its transformation, although movement generally occurs only in response to stimulation, such as its being touched or placed in direct sunlight.
The beetle that eventually emerges is light beige, darkening to red, brown, and finally black after about two days.

Feeding Your Mealworms

Any type of cereal bran or meal (wheat, corn oat, rice, etc.) can be used as your mealworms’ main food source. If you are setting up a small colony, you can even grab some oatmeal, corn meal, cream of wheat or bran flakes from your pantry. You can purchase oat bran in the breakfast cereal or baking section of the supermarket; I have found that I can buy wheat bran out of a bin at my local feed and pet store for about 20 cents a pound.

You may want to fortify the bran or meal to increase the vitamin and mineral content of the mealworms, especially with respect to calcium. Frye (1992) recommends adding 15 percent alfalfa flakes, 20 percent high-protein baby cereal, and 15 percent dry poultry mash. Raw apple, potato or carrot provides some moisture and nutritional value as well. Be sure to include one of these, especially when the beetles are being fed.

Many mealworm species do not require drinking water. They can absorb water from air with humidity as low as 30 percent. If you live in a humid area, you won’t have to provide your mealworms with water. If you live in a dry area, mist their container every day or two, but avoid using so much water that the bran or meal becomes wet and moldy.

Maintaining a Colony

A start of a Tenebrio molitor colony is easily obtainable at pet stores that cater to reptiles and amphibians. You probably won’t be able to catch your own darkling beetles or mealworms, unless you have access to a granary.
A flat, broad container made of metal, plastic or glass works well for raising mealworms I find a sweater box works well. A one-gallon container is sufficient for a start of 50 to 200 mealworms. Use two or three inches of bran or meal for substrate and food. Sterilize the bran or meal at 200 degrees Fahrenheit for two hours to kill grain mites and meal moth eggs.
Cover the substrate with three or four layers of burlap or newspaper. When misting the container, only mist the burlap or newspaper, keep the bran or meal dry. I prefer burlap, because mealworms can easily crawl through the holes, making it easier for them to get to their food. Mealworms are poor climbers, and the beetles seldom fly, so the colony container can be left open as long as the sides are slick. I would suggest covering the container with a screen to keep other insects and the cat out of it anyway.
Once the colony is set up, the only care it will need for some time is a daily misting, but only if the humidity is below 30 percent. Remember, do not overwater! Too much water in one spot will cake the bran underneath, and encourage the development of mold. Change the potato, apple or carrot when it gets moldy or dries out.
Keep the colony in an area where it will receive a normal day/night light cycle. High temperatures of over 80 degrees Fahrenheit are not necessary, but they do speed up the life cycle, which results in increased production. Tenebrio can withstand night temperatures down into the low 40's.
A powdery waste from the bran eaten by the mealworms will accumulate. By the time this waste has become excessive, the mealworms should be large enough to stay in a fine sieve, so sifting can clean the container. However, a drawback to a mixed culture is that it contains everything from eggs to beetles, and sifting to remove waste means that eggs and small worms will go through a fine sieve and be lost. This could be tolerable if you have more than one colony, or just use mealworms for supplemental or emergency feeding.
To start new colonies, or for quantity production, remove pupae from the colony as they form, and transfer them to prepared containers in lots of 100 or more. Moving at the pupa stage is easiest, I believe. There, the adult beetles will emerge at about the same time, mate, and deposit eggs and die. If you only have one generation in a colony and remove all pupae to a new container as they form, you can easily put off cleaning the colony until the mealworms are large enough to stay in a sieve.
Mealworms are normally refrigerated in a container with air holes at 42 to 56 degrees Fahrenheit, where they will become dormant. They can be kept this way for several months.

Feeding mealworms to Your Fish

Mealworms tend to gather between the layers of burlap or newspaper within their colony’s enclosure, and can be scooped up by hand or picked out with forceps. They can be coated with liquid or powdered vitamin and mineral supplements, and then hand-fed by placing directly into the mouth of your fish. That way the supplements are less likely to get washed off.

Mealworms are generally serviceable as food, but their horny outer covering may affect the intestinal tracts of some fish if they’re the only live food being offered. You can minimize any problems by feeding only the recently molted, white soft worms.

Mealworms do not live long within an aquarium filled with water, and unless uneaten worms are picked out, they can foul the water and provide a start of an ammonia explosion.

Obtaining a starter culture

The larva of the Tenebrio is most commonly used to feed to a wide variety of reptiles and amphibians, and birds kept in captivity. You can purchase Tenebrio in the pet store or by mail order. The larvae are about an inch long, and they are a golden yellow color.

Keeping and Breeding Tenebrio

When you purchase Tenebrio from the pet store you may be instructed to keep them in the refrigerator. You may do this if you like, but the growth of the larvae will slow down and you will likely never be able to breed the mealworms while they are in the fridge. Also, if the mealworms are kept at room temperature they will eat, and if you feed them a good diet you can be sure that your pet fish is getting a nutritious meal when you feed him the mealworms.

Here is how I keep and breed mine:

1. Obtain a shallow Tupperware or Rubbermaid container.
2. Put lots of air holes in the lid, or cut out a large portion of the lid and use a hot glue gun to glue some fine window screening material to the inside of the lid around the hole.
3. Fill the bottom of the container with a substrate of rolled oats or bran a couple of inches deep. The mealworms will eat this.
4. Put one small shallow dish in the bottom of the container. I use the tiny tinfoil potpie plates. Fill these dishes with a half of a potato, a chunk of carrot and if you like a 1/4 to a 1/2 of an orange. Other veggies can be used. The mealworms will eat these and get their moisture from them so you may want to also sprinkle the veggies and fruit with calcium and vitamin supplements so that the mealworms will be a wonderful healthy meal for your fish.
5. Change the veggies every couple of days. They will go bad and mold. Mold and dampness will kill the mealworms.
6. The Tenebrio will eat and live for a long time in these containers when kept at room temperature. Eventually you will notice that some of the mealworms metamorphosis into pupa, and the pupa into beetles. The beetles will mate and lay eggs in the substrate or on a porous piece of wood in the container. They will cycle themselves with little help or bother from you. All you have to do is feed them.

If you do decide to Keep and breed King Mealworms (Zoophobas) here are some differences to be aware of:

Keeping King mealworms is very similar to keeping Tenebrio at room temperature. Please follow items 1-5 as above except that if you will be keeping large quantities of mealworms on hand you may want to use a deeper Tupperware or Rubbermaid container.

Breeding them is, however, a different story.

Here is how I breed mine:

1. If you would like to have a modest supply of Zoophobas around that you have bred yourself select ten mealworms from your stock. You may select more or less if you like, but I would use a minimum of six to begin with, as they don't always survive.
2. Collect film containers, pill bottles or other similar small lidded containers. Puncture several small holes in each lid, and fill each container half full with bran.
3. Place one king mealworm in each container and close the lid securely.
4. Place the containers in a warm area, preferably an area that stays at about 80oF most of the time. I used a breadbox over my fridge.
5. Check the containers at least once a week. If the mealworm is inactive and is straight it is probably dead. Remove any dead mealworms that you find and replace them with new ones. After the first or second week you will see that the mealworms have become inactive and curled up in a ball. This is fine. They have begun metamorphosis.
6. By the second or third week most of the mealworms should have turned into large white pupa. The pupa will not move much, but it will wiggle when touched or disturbed.
7. Between the third and fourth week the pupae will morph into large beetles. The beetles are white when they first emerge but quickly turn pink, reddish brown then black within the first 24 to 36 hours. Check your containers daily between the 3rd and 4th weeks.
8. Place the beetles in their own Tupperware container (as described above) with bran for substrate, a small dish of fresh veggies, and a piece of porous wood (cork bark?) on which they can lay their eggs. Keep the beetles in a warm (high 70's to low 80's F.) room for best results.
9. The beetles will begin to lay eggs within the first couple of weeks.
10. After approximately a month of keeping the beetles you will begin to notice microscopic mealworms (larvae) amongst the bran.
11. Within two months after creating your beetles you will have a number of half size and full size mealworms in the container. You can put your mealworms in a separate container once they are large enough to be easily seen and picked from the substrate.

Good luck feeding your large fish this excellent food source.


Frye, Fredric L 1992 Captive Invertebrates: A Guide to Their Biology and Husbandry. Krieger Publishing Company.

updated 30 June 2003,1909, BL