Raising Mealworms for the Birds

My step-lizard was 2 years old when my husband and I got married and my husband has always fed him mealworms as an occasional treat (he mostly ate veggies) so we have been familiar with mealworms for some time, though we’ve never dealt with them in quantity.  Now that we have ducks and chickens and we are moving toward providing them with primarily homemade food, rather than feeding them a pre-mixed ration, we are thinking about raising protein to meet their winter needs when there aren’t so many wild bugs for them to find. Although we do give them some red wrigglers from our compost worm farm, they don’t seem to find them very exciting and we thought they might want a little crunch too, so about a year ago, we added mealworms to the farm.

What are Mealworms?

Mealworms are the larval stage of the darkling beetle Tenebrio molitor. They feed primarily on grain and can become quite a nuisance if they get into grain stores. However, these darkling beetles cannot fly and so can be contained quite effectively to produce an ongoing supply of mealworms that gets replenished about every 3-4 months.

Mealworms are not only useful treats for chickens and lizards but are human edible too, with a nutrient profile that rivals that of beef. Dried mealworms can be ground into flour for a protein boost to baked goods. I am not ready to take that step, but it’s nice to know that we’ve got options when the zombie apocalypse happens.

Mealworms are readily available at most pet stores, but you can also order mealworms online.

Setting Up the Mealworm Habitat

A container for the mealworms just needs to be large enough so they can wriggle around and not be all over each other and have enough substrate in the bottom that they can burrow completely down into it.  The sides should be smooth plastic or glass to prevent escape and but I find the lid isn’t really important if your sides are tall enough because they don’t tend to fly. There is some argument as to whether they can fly or not. I have never seen them do it. Drill holes into the top for ventilation or use a screen mesh lid. Ventilation is important to prevent mold. This habitat should be placed somewhere out of direct sunlight.

Feeding the mealworms

Mealworms are kept in a substrate of food. Any grain will do, old-fashioned rolled oats and wheat bran both work very well, but we’re going to eat oatmeal and we’re not going to eat bran, so if I’ve got bran from processing wheat, I will use that. I have also used expired cornmeal and chicken feed, in a pinch. These all worked just fine. If you’ve got big bits (as in rolled oats) you might want to run them through the blender to break them down so that later, if you want to use a screen to separate your worms from the substrate, your substrate is actually going to flow through the screen.  Mealworm bedding and food from a pet supply store may have been treated with hormones to keep mealworms from maturing, so you’ll want to discard whatever substrate came with them when you move them into their new home unless you’ve had that discussion with your pet store guy.

In addition to the grains they live in, a daily slice of fruit or vegetables will keep them hydrated. I am told that this supplemental feeding is unnecessary, but it increases their productivity and reduces the likelihood of cannibalism. I think a few kitchen scraps is worth that. Besides, they really like it.

When I first brought home my 100 pet store mealworms, I gave them a couple of ends that I snapped off some green beans, thinking I was giving them to them primarily for moisture, but they soon swarmed them and by the next morning, my 100 little mealworms had consumed them completely! So I give them a bit of the green scraps from a cauliflower, by the end of the day, these were gone; a strip of banana peel came next, then a couple of potato peels- they eat anything, including meat.

Mealworms are a good help at cleaning off skulls and such for projects, but they take their sweet time about it. I first scrape as much meat off the bone as I can manage and let them sort out the fine detail. I have not done a scientific study but just based on casual observation, the presence of a bone seems to cause s a population explosion- though it could just be that more worms and beetles are visible when there’s a bone to be cleaned than when it’s just a boring old potato.

Mold can be a serious problem in your mealworm habitat, so keep an eye on these treats and remove anything they aren’t eating quickly or that’s starting to look off.

The Mealworm Lifecycle

You probably got your mealworms in the larval stage of their lifecycle.  Before your mealworms breed, they will have to metamorphose into adult darkling beetles. This takes about 8 to 10 weeks, though it may be shorter for you if your mealworms were older when they came to you. Mealworms primarily eat and grow during the larval stage. They will molt several times, about 15, before they turn into pupae. Mealworms turn quite dark before they molt and will be pale and soft immediately after the molt.

When they are ready to pupate, they will have a final molt to reveal a white alien-looking creature with stunted legs and wings. Looking closely, you’ll just be able to see little dot eyes. These do not eat, but might wiggle a bit. They will stay like this for about 2 weeks, maybe a little longer or shorter, depending on the temperature and humidity, before emerging as adults.

 

Mealworm pupa.
Mealworm pupa.

Once they reach adulthood, as small, black, flightless beetles, they will spend a few weeks maturing and flirting. The males release a pheromone to attract the females and females have been observed to be more receptive to the pheromones of males who are not from the same lineage as themselves. (Thus it may be a good idea to maintain more than one colony to switch things up and keep things interesting, though most people have no problem getting them to breed anyway.) After about 3 weeks, the females will begin laying eggs in the substrate, about 500 each. These eggs take about 2 weeks to hatch but may take more or less depending on the conditions.

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Adult darkling beetles enjoying a salad.

Cannibalism

Mealworms will cannibalize each other. The worms and adults will attack each other and the pupae and the eggs. There are a few things you can do to prevent this. The first step is to make sure they receive their daily treats so they can stay well-hydrated.  It helps to provide lots of “cage furniture”- bits of cardboard, egg cartons and other things they can hide in so they’re not on top of each all the time. Of course, it is important that your enclosure be big enough to accommodate everyone as well.

You can also separate the various growth stages and keep the adults and the larvae separated. The easiest way to do this is to move the pupae gently to a new colony so that they can continue to pupate in peace, then move them again when they darken and show signs of maturity to a breeding container for the adults.  Some people go a step further, straining the substrate in the adult container periodically to separate the eggs as well. Some people do none of these things and still get plenty of mealworms.

Keeping things Clean

I empty out my mealworm bins and give them a good scrubbing every few months on a rotation (see below in the Breeding section). Beyond that, I do a weekly maintenance of removing uneaten bits of food, and pulling out likely looking worms for the freezer and moving adults into the breeding bin and removing spent pupae shells and dead beetles.

You should be aware that mealworm frass is rather allergenic. Inhaling the dust or getting it on my hands and touching my face makes me somewhat uncomfortable. It isn’t as bad as rabbit urine, but it’s still worth wearing gloves and a face mask, or at least make sure you have good ventilation and wash your hands thoroughly afterward, if you are, like me, the type of person that only thinks about protective equipment after her eyes are burning.

Breeding Mealworms

Mealworms will grow and reproduce fastest at a temperature of about 75 degrees Fahrenheit with a relatively high humidity, but if they are kept at normal household humidity and room temperature, they will still grow at a moderate rate.  If you wish you raise the heat, you can do so (carefully) with a ceramic heater or an under tank heater. Giving them a ration of fresh fruits or vegetable bits every few days will keep their humidity in a pretty good range, but if you feel this is not sufficient, you can raise the humidity by putting a jar of water in the habitat, just make sure the mealworms can’t get into it because they will drown themselves.  You can also use a moist sponge, but be aware that they are a haven for bacteria. I do not personally provide any supplemental heat or humidity for my mealworms, I just keep them in the house.

Your mealworms, if kept warm, fed and clean will grow, pupate and breed in a single container, but it may be difficult to keep them clean and to harvest mealworms at just the right time with all those generations running about together. Because of this, many mealworm breeders have set up a multi-box system and I have done this myself. My system is a little complicated, but it reduces cannibalism by keeping critters of approximately the same size together and providing some protection for eggs and pupa and it provides a built-in cleaning and harvesting schedule.

My mealworm breeding system.

The four box method works right for me, though there are certainly other methods. These boxes are just about right. Start with one box for your mealworms, put about an inch of grain substrate in the bottom and place the mealworms on top. Discard the substrate they came with. They will burrow down into the substrate and you won’t see much of them after that except for when they are swarming a tasty bit of potato until they are ready to pupate.

When you begin to see pupa resting on the surface of your substrate, set up a second box just the same as the first. The pupa will soon turn into adults which spend more time running around on the surface, so you may wish to give them toilet paper rolls, bits of egg carton,  bits of hay, sticks and other things to climb about on and hide under. Place new pupae in the second box and allow them to hatch into adult beetles (in 1-3 weeks) and begin breeding (in another 2-3 weeks).

Once you have several adults running around in there, start a third box for new pupae.

When baby mealworms start showing up in the first breeding box (Box #2), I move the adults into a fresh breeding box (Box #4). I toss any dead beetles into my chicken feed for extra crunch. The box I just moved the adults out of (Box #2) should be full of eggs and baby mealworms, I continue raising them and move pupae into Box #3 until I start seeing babies in that box, then I move all the adults into the box with the other adults (Box #4) and am left with a second box full of eggs and baby mealworms.

By this time, all of the original 100 or so mealworms we put into the first box have probably either pupated or died, so we can empty it, scrub it and start a new box to put pupae in from the two worm boxes (Box #2 and #3).  (So to review, we have worms growing in Box #2 and #3 with pupa from each going into box #1 and adults breeding in box #4.)

The rotation continues- When we see babies in box #4, we move all the adults into box #1 and stop putting pupa in it. If there are any worms left in Box #2 at this point, they should be of considerable size, so we’re going to harvest and refrigerate them or give them directly to the birds, empty out the box, give it a good scrubbing and set it up for new pupa. (We now have worms growing in boxes #3 and #4 with pupa from these going into box #2 and adults actively breeding in box #1.)

In summary, any pupa goes into the younger generation adult box. When worms become evident in the older generation adult box, we move all the adults into the younger generation adult box and it becomes the older generation adult box and the previous older generation adult box becomes the younger generation worm box. The oldest worm box gets harvested, cleaned and scrubbed and becomes the next younger generation adult box.

If at any point you find that you’ve got way more mealworms than you will ever need, you can start feeding some of the adult beetles to your chickens too.

 

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