How to raise mealworms (Tenebrio molitor)
Everyone who has a small flock of chickens should raise mealworms. It's very easy to do and once set up they are virtually maintenance-free and very inexpensive. I give my girls a hand-full or so a day; they think fresh mealworms are the best treat in the world.
1. You need a container; I prefer 10 gallon aquaria. They allow you to see the condition of the substrate and the glass keeps them from climbing out. You can also use a plastic tub. Keep in mind that it is better to have greater surface area than depth. Never cover it with anything that restricts airflow, especially if you live in a humid environment; but a wire cover is good to keep the lizards and geckos from eating everything if you keep it outside.
2. Add about 3" of wheat bran to the bottom of the container. I get mine at places that sell it in bulk, but you can also get it at feed stores. You should get it for $1/lb or less (buy about 4-5 lbs to start). You can also use chicken feed, provided it does not have diatomaceous earth (DE) added. I would highly recommend freezing any grain product for a couple of weeks or heating it to 130 degrees for 15 minutes prior to adding it to your colony to limit unwanted pests.
3. Add some mealworms, the more the better and the faster the start-up will be. I recommend starting with at least 1000 for a container the size of a 10 gal. aquarium.
4. Add some vegetable matter. I use potatoes, apple peals, watermelon rinds, whatever kinds of scraps are available. Feed them as often as you'd like. The more you feed them, the more they multiply. You don't want it to ever get wet inside, the wheat bran must remain dry. Most colony failures are a consequence of excess moisture, which can spark outbreaks of fungus and mites. I live in one of the driest places in the world and I never add moisture beyond that contained within vegetable matter--and I also avoid adding high water content vegetables. The more varied the diet, the better the worms are as food. Be observant when adding new foods and immediately remove anything that they won't eat to avoid rot. I also add a couple cups of oyster shell which can significantly increase calcium content of the worms.
5. Keep your colony in the shade, outside heat (even in Arizona) is great for them but direct sun or rain will kill them. The warmer they are kept, the faster they develop. They must be brought inside for the winter as their development will slow considerably and they will die in a freeze.
6. When the wheat bran particles start looking smaller and the layer gets thinner, add more (just dump it over everything). I add more a few times a year. I only clean up the dried vegetable matter that builds up, very rarely the bran. The colony below is over 20 years old and I've only removed the old bran a few times.
7. Wait a couple months after setting up your colony before you begin using worms for food. Use only the larvae (worms) to feed your birds. The pupae and beetles should be left alone for reproductive purposes and never removed from the colony. Old carcasses will be consumed by successive generations. You can collect worms when you add new food. For example, cut a potato in half, put the cut side down and wait 10 min. or so. The larvae will grip on with their mouths and you just lift them up and shake them into a container. Remember, they are harmless and don't bite.
8. Some people separate beetles, pupae and larvae--I don't, mostly because production is fine for me without the extra effort. If you provide adequate resources for the colony, cannibalism is very low. However, separating them is a good way to observe development--which is very interesting.
9. Because reproductive and developmental rates are higher with greater temperatures you'll often have more worms in the summer than winter. You can extend the summer glut of worms by packing them in fresh bran and storing them in the refrigerator for later use.
A word of caution: With prolonged or frequent exposure to mealworms, some individuals will develop severe allergies to them. I highly recommend wearing a mask while tending to your colony and be observant of any respiratory changes you might experience while working with it.