Lesson #2: Feeding and hydration

>> Feeding mealworms keeps our workload to a minimum. The exception is regular hydration of the larvae.

The larval food is based on the cereal-based substrate as described in the previous chapter. However, like all creatures, our mealworms need for optimal development an adequate supply of fluid.

Mealworms – feeding

If the mealworms remain without water for an extended period, their growth will slow down significantly, even though they won’t die. There are studies that have shown that mealworms can absorb water through the moisture in the air (vaporization). However, this is associated with energy loss and increased food consumption. Thirsty mealworms can be easily recognized by how they gather around offered fruits, leaving only the peel of a sliced apple by morning.

You can add fluids that are primarily plant-based, such as vegetable and fruit scraps. Carrots, potato peels, squash leaves, and even dandelion greens are popular choices. Feel free to experiment with other options that come to mind. Remember that mealworms won’t consume anything too hard, which can lead to extra work during sorting. Be cautious about using store-bought produce, as the surface might be treated with pesticides; it’s better to thoroughly wash them.

mealworms feeding

Mealworms – feeding

We can also add some moisture by lightly spraying the substrate a few times a week using a regular water spray bottle. However, it’s better not to overdo it. The reason is – the substrate should always stay dry and non-sticky. If we exceed the supply of vegetables, spoiled leftovers that are not consumed will have to be removed manually.

If the larvae are still small (under 5 mm = 1-5 weeks), it doesn’t make sense to add moisture in any other way than by spraying, as added food pieces would either mold or dry out.

The rearing box should not be sealed. Without air circulation, the substrate could eventually turn into a sticky mass full of mold.

Online shop – water crystals

Insects can be easily hydrated with water gel – instructional video included.

Insect Water Crystals


The larvae can utilize approximately half of the food’s weight to build their bodies. What happens to the other half?

After several days to weeks, it’s hard not to notice that the substrate begins to change its structure. It transforms from a diverse mixture into a powdery fine homogeneous golden powder – these are millions of insect excrements, or, in other words – frass.

Insect fertilizer Frass

When most of the substrate has been consumed, and the larvae have had their feast, it’s time to do a little cleanup. Insect excrement, with a diameter of up to 0.3 mm, can be easily sifted from the substrate using any fine sieve. It’s been proven that a high frass content in the substrate slows down the growth of the larvae. So sieving is best done every 14 days in the second half of the rearing period.

Frass is a significant bonus in mealworm farming. It’s an excellent organic (natural) NPK fertilizer, and unlike the waste of other livestock, insect excrement is dry and odorless.

Frass contains a wide range of minerals that your plants will enjoy. Additionally, it contains chitin, which positively stimulates their defense mechanisms against various pests. With frass, you can, for example, get rid of aphids. You can either mix the fertilizer directly into the soil of your plants or dissolve it in water for irrigation.

Insect Frass – Organic Fertilizer

The various uses and all the benefits of insect frass are thoroughly discussed on the website Hnojík.cz

Melaworms feeding - frass

Loss and Diseases

Mealworms are indeed very resilient, and I would estimate the mortality in their breeding to be certainly less than one-tenth of percent. Nevertheless, with such vast numbers of individuals being raised, it occasionally happens. It is better to regularly remove the deceased individuals to prevent the source of mortality (whatever it may be) from spreading further. Most of the time, mechanical damage (careless handling during sorting or cannibalism) or excessively high temperatures are the causes, but insects can also suffer from diseases and parasites. Experienced breeders recommend not underestimating these issues. Deceased comrades can be easily recognized within the group by their significantly darker color at first glance.

Harvesting >>

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