How to make Flake Soil for Beetle Breeding
Japanese Rhino Beetle larvae (Trypoxylus dichotomus) on Flake Soil
General Information
This in-depth Flake Soil recipe of mine was originally developed in mid-2010s, and was shared among private hobbyists. In 2020, I compiled my accumulated experience into this official online guide with the aim of making beetle breeding more accessible to beginner hobbyists. Many new recipes derived from my original guide here have appeared throughout the web since then, which I am very happy to see as it is evidence that more people are getting involved in this hobby!
As this is the original recipe which many later recipes online have been based on, please feel free to contact me if you have any questions regarding the information presented here, or if you would like advice on the safety and suitability of new additives that some modern guides now include.
What is Flake Soil?:
Flake soil is a type of highly regarded substrate that is suitable for the rearing of beetle larvae, and also for other types of invertebrates kept in the hobby such as isopods and millipedes. It can be produced at home by adding various additives to sawdust and allowing the mixture to ferment over tim, until it turns into a uniform, soil-like substrate. Flake Soil is the go-to substrate for advanced breeders, as it outperforms conventional leaf litter or wood-based substrates collected from nature, in terms of larval growth rate and final adult size.
When using substrates collected directly from nature, different materials are typically required depending on the beetle group. For example:
Leaf mulch for Cetoniinae (flower beetles)
Well-decayed wood for Dynastinae (rhinoceros beetles)
Moderately decayed wood for Lucanidae (stag beetles)
With Flake Soil however, this complexity is eliminated. It provides a single, versatile solution suitable for all three groups listed above, with nutrient levels that can be carefully controlled during preparation to promote healthy larval development as it is prepared from scratch at home. For a detailed breakdown of traditional, nature-collected substrates used for each beetle group, see my Beetle Substrate Guide.
Boxes of fully fermented Flake Soil
Why Fermentation is Essential:
Larvae of most Cetoniinae, Dynastinae and Lucanidae species obtain their nutrients primarily from a structural compound found in wood called cellulose. Raw, unfermented sawdust cannot be used for beetle larvae because wood also contains lignin, which is another structural compound which is very tough and provides trees with rigidity and strength. Lignin prevents larvae from accessing the cellulose present in fresh wood. As beetle larvae are unable to digest lignin on their own, the cellulose they require remains effectively “locked in” within the wood by the lignin. During sawdust fermentation, microorganisms break down the lignin structure, thereby unlocking the cellulose so that it can be digested and utilised by the larvae.
As fermentation progresses, both the colour and smell of the substrate change:
Colour: light yellow → brown → dark chocolate
Smell: sweet/alcoholic → yoghurt-like → earthy soil
These changes provide useful indicators of fermentation progress.
Additives in Flake Soil?:
Flour is the core protein additive used when making flake soil. For advanced breeders, additional additives may be incorporated depending on the desired outcome. These can include wheat bran, soy flour, buckwheat flour, chitosan, or royal jelly, among others.
For beginners, I strongly recommend using plain white flour only. While other types of additives (such as soy flour) can be more nutrient-rich and increase the nutritional value of flake soil, they also significantly increase the risk of fermentation failure and rot. In simple terms - the higher the nutritional content, the greater the risk of rot instead of proper fermentation.
It is important to understand that the raw additive itself is not directly consumed by larvae. The purpose of the additives in the production of flake soil Is to stimulate microbial activity and aid in the fermentation of the wood, while incorporating the nutrients into the substrate through bacterial processing. Additives must always be used in moderation. Based on my experience, the total weight of additives should not exceed 8 % of the total Flake Soil volume. Excessive additive levels can shock larvae, dramatically increase mortality rates, and lead to long-term health issues such as weakened immune systems or deformities during pupation and adult emergence.
My Tried and Tested Recipe for Flake Soil Substrate:
The following ingredients are the measurements requiered to make 10 L of flake soil.
Ingredients:
For main substrate mix:
10 L sawdust mixture (80% sawdust 20% frass / old flake soil)
200 g flour
50 g sugar
For yeast mixture:
10 g brewer’s yeast
5 g sugar
500 ml lukewarm water
Method:
Measure and weigh all ingredients accurately. Mix the sawdust, flour and sugar together in a large tub.
In a separate container, dissolve 10 g yeast and 5 g sugar in 500 ml lukewarm water. Stir well to dissolve the yeast and sugar, and allow the mixture to stand for 30 minutes to to activate the yeast.
Pour the activated yeast mixture into the sawdust blend and mix well.
Gradually add water until the substrate is moist but not saturated. The correct moisture level is reached when a squeezzed handful of sawdust holds its shape without water dripping out.
Flatten out the sawdust mixture.
Place the lid on the tub and store the container in a location with a stable temperature above 23 °C, where fermentation can occur reliably.
After 1 week, mix the substrate thorouhly. At this stage, fermentation will have already started, indicated by the alcohol-like smell and heat generation due to bacterial activity.
Continute mixing the substrate well every 2-3 days to introduce oxygen evenly throughout the substrate. Fermentation is complete once the substrate smells like rich, earthy soil. Under my conditions, this usually takes around 1-2 months. Warmer temperatures may shorten this period and cooler temperatures may extend it.
Optional Additives for Advanced Breeders:
Cellulose
Chitosan
Trehalose
Milk protein
Soy protein
Glutamic acid
Richard’s Flake Soil Making Tips & Precautions:
Flake soil is easier to produce in summer than in winter, as the bacteria that break down the sawdust and process the additives are more active at higher temperatures.
Excessive moisture is the most common cause of failure. Too much water can create anaerobic pockets of substrate, leading to rot. Excessive organic additives can also promote the growth of other unwanted bacteria, causing rot instead of fermentation.
If the substrate smells of vinegar, ammonia, or faeces, it is a sign of fermentation failure. If this happens, it is recommended to start over from scratch with less water and less additives. In some cases, where the rot was caused by excessive substrate moisture, the subsrate can be salvaged by fully drying it out to eliminate unwanted rot-causing bacteria, then rehydrated and fermented again with less water.
Beginners should stick to plain white flour as the sole additive. The higher the nutrient content of the chosen additive, the greater the risk of failure.
Higher additive levels generally produce larger adults, but excessive levels will dramatically increase larval mortality.
The microorganisms responsible for fermentation require oxygen. Therefore, it is important to mix the substrate thoroughly every 2-3 days once fermentation has kick-started.
It can be difficult to judge the correct moisture level when making flake soil for the first time. If there is too little water, fermentation will not start. If there is too much water, the substrate will simply rot instead of fermenting. It is much easier to add more water than to fix an over-saturated substrate.
Even after completion, flake soil can continue to ferment slowly. For long term storage, fully dry the flake soil to halt micorbial activity. Before use, simply rehydrate to the correct moisture level.
