Lesson #5: Parent breeding box

>> Egg laying is ensured by the parent breeding box specially designed for the efficient separation of mealworm beetles from the laid clutch and its easy harvest.

Gender of beetles

The gender of beetles cannot be distinguished by the naked eye. Both genders are equally represented in the population in a 1:1 ratio. Mealworm beetles become sexually mature just a few days after hatching. Females are then capable of laying 160-320 eggs within the following 6-8 weeks. I found a source that even mentions up to 1000 eggs. The yield we achieve will depend on the conditions we provide to the beetles. In my opinion, with a little care we can easily surpass the relatively low efficiency of large-scale breeders, who have to return 10-15% of the larvae to the parent system. Of course, only if we believe it’s worth the effort.

Mealworm egg laying box

Mealworm egg laying

Separation of the clutch

To prevent cannibalism among the beetles on their own clutch, we need to separate them from it. Scientific studies show that the efficiency of a separated parent system is many times greater than an unseparated one, especially if we harvest the substrate with the clutch at longer time intervals. To separate the beetles from the laid clutch, we use a so-called parent system. We can make it ourselves if we are skilled enough, but it’s not a simple matter, as the beetles’ escape ability is legendary.

The parent system is essentially a plastic box, whose bottom is replaced by a sieve, and then it is placed on a tray with substrate.

mealworm breeding box

Parent system

To make this, we will need a high-quality wire mesh with a mesh size of 1-3 mm. Ordinary insect screens won’t hold the beetles for long. You will also need two plastic boxes that can fit inside each other. If you don’t have such boxes, you can make the bottom box from a cardboard box of the appropriate size. It won’t contain any larvae or beetles, only the substrate with the eggs, so there are no special requirements for it.

Cut out the bottom of the inner box and replace it with a wire sieve. A proven way to connect them is by using a hot air gun. It’s important not to leave weak connections or even larger holes for the beetles to escape. You can forget about any adhesives or adhesive tapes because mealworm beetles are too nosy. Pour a 1-2 cm thick layer of substrate In the bottom plate (or tray) and place the inner box with the beetles on it.

Substrate layer

The beetles lay eggs using a long ovipositor. It allows them to place the eggs through the sieve into the substrate without being able to consume them. If the substrate layer is too thin, the females can reach the bottom of the outer box with their ovipositor, where the eggs will stick. Sticked eggs cannot be removed without destroying them. I tried placing a paper lining at the bottom, but it is not easy to handle. A sufficiently thick layer of substrate is the most convenient way to ensure that everything “runs smoothly”.

Online shop – Mealworm breeding box

Breeding box for adult beetles. The system is designed for maximum efficiency in laying eggs into the substrate and their easy harvest – watch the instructional video.

potemník moučný rozmnožování

Mealworm egg laying

Population Size

You can determine the population density of the parental system yourself. The optimal ratio for egg-laying efficiency is one beetle per 5 cm2 of space (= 500 beetles per 60×40 container). On the other hand, the more beetles you have, the more eggs you will obtain in absolute numbers. Large-scale breeders may have up to 10 times more beetles in the parental system. However, the relative efficiency decreases significantly with overcrowding, not to mention the stress on the inhabitants. 500 adult beetles are also the minimum number that ensures sufficient genetic variability of your breeding (sufficient gene pool = a healthy population). You can easily increase the living space for the beetles by adding several paper egg cartons.

mealworm laying eggs

Mealworm egg laying

Beetles have the same diet as the larvae, although they don’t consume as much. We can spread a layer of substrate on the sieve for them (they love to burrow in it). Cut up an apple, potato, or carrot, and scatter a few pieces of stale bread. Unlike the larvae, beetles cannot absorb moisture from the air, so if we expose them to thirst or hunger, their fertility will decrease.

Egg harvesting

With the parent boxes, it’s important to keep track of when we placed the beetles in them. After 8-9 weeks of life, their active reproductive careers come to an end. So it will be necessary to replace them.

We harvest the contents of the lower box once or twice a week. Carefully transfer the substrate with the laid eggs to another box. We’ll mark its laying date, in a few weeks, a new generation will begin to swarm here.

The question of how many eggs the parent substrate will contain after a week has only a theoretical answer. On average, one female lays 20-40 eggs per week in weeks 2-9 of her life. Multiply this by the number of beetles in the box, divide by two (since there are equal numbers of males and females), and you get a rough estimate. With 500 beetles, this theoretically amounts to 5,000-10,000 eggs per week. This estimate is, of course, very rough, and the actual number may vary for various reasons. Experience will show us how well we’ve managed and calculated.


The internet claims that mealworm beetles don’t fly, but that’s not entirely true. Under normal circumstances, you don’t have to worry about these beetles swarming around your home. If nothing is lacking for the beetles and the walls of their box are slippery enough for their little legs, they won’t leave it. However, on one extremely hot summer day, I witnessed a series of clumsy take-offs with my own eyes. In general, it’s best to avoid temperatures above 30°C when rearing them. During such weather, it’s a good idea to keep the windows closed during the day and ventilate at night when it’s cooler.

New generation

The new larvae begin hatching from the laid eggs in the substrate after about 10 days. They are only about 1.5 mm in size and won’t be easily visible to the naked eye until a few weeks later. In lower temperatures, it may take even longer. Don’t panic – they are there! The first evidence of the presence of these small larvae is the number of small, reddish skins on the surface of the substrate.

Until the larvae grow to 5 mm size, you should handle their box as little as possible. “Baby” larvae are vulnerable, and you don’t want to unnecessarily reduce your breeding stock. Until then, you should also ightly humidify the box 2-3 times a week only using a spray bottle.

Rozprašovač na vlhčení substrátu

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