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Make Flake Soil for raising Beetle Larvae

Beetles and beetle larvae are very easy to keep and raise, but the most effort and road block for new Australian beetle keepers will be flake soil. What is flake soil? It’s the fermented wood required to feed certain species of beetle larvae. These larvae survive exclusively on decomposing wood until they pupate and become adults, who then eat a sweet diet rich in sugars and fruits. Unfermented wood that is yet to decompose is too difficult for many beetle larvae to eat, so it must be broken down by fungi through fermentation. 

Other groups of invertebrates may benefit from having flake soil in their substrate and diet, such as isopods and millipedes.

A well developed rhinoceros beetle grub on top of some flake soil substrate that has been mixed in with previous substrate that it was delivered with. 

Flake soil is not easy to come by, as no pet chains offer it, and it can be difficult to harvest uncontaminated soil of the right composition from the natural environment. It can be found in specialist stores, but for many people it is most practical to make their own flake soil. Flake soil takes time to make, and can be expensive if you are buying flake soil for the entire lifespan of a beetle grub. Anyone can make their own flake soil, so long as they have outdoor space. 

We do offer flake soil on our webstore in case you are in a pinch and need some urgently, or cannot make your own due to circumstances (such as living in an apartment with no outdoor space for making flake soil). 

How to make flake soil

Ingredients and tools

  • Oak, Cherry or other hardwood pellets (from any bbq store)
  • A large bucket
  • Hot/Warm Water
  • Active Baker’s Yeast
  • Wheat Flour (can be swapped out with bran)

Getting the fermentation started

  1. Fill the bucket to 1/4th with wood pellets. Note down the weight of the pellets used in the bucket. Eg. If you used 1kg, note it down for later steps. 
  2. Very slowly add warm water into the bucket. The pellets will begin to expand and become loose wood flakes. Hot water will work faster, but be mindful not to scald yourself and to let the mix cool down before moving on to next steps. The flakes should be loose and moist, but not so wet that water can be squeezed out of it. Substrates that are too wet will not ferment properly.
  3. Measure out some wheat flour. How much flour you add to this substrate will depend on the weight of the wood pellets you originally used. For every 1kg of wood pellet used, you will need 100g of flour. 
  4. Add and mix the flour into the wood flakes bit by bit until it is evenly mixed with no clumps of flour showing. 
  5. When the mixture is around room temperature, sprinkle and mix in active baker's yeast. 
  6. Place the bucket in an outdoor area that is protected from the weather, such as a greenhouse, garage or covered balcony. 

Maintaining fermentation

  1. Make sure to mix the fermenting flake soil every 2-3 days to keep it well oxygenated. If it feels dry, add a little water and mix to keep it moist.
  2. Fermenting flake soil that needs to be mixed more will smell like wine or vinegar. 
  3. The longer the mix ferments, the darker brown it will become. 
  4. When the flake soil is ready, it will be dark brown and will have a faint earthy smell. For rhinoceros beetle larvae, it will be closer to the color of garden soil. 
  5. The entire process of fermentation can take several months. For most keepers, 2-3 months of fermentation is sufficient for stag beetles, and 4-6 months is sufficient for rhinoceros beetles. This time varies depending on climate. Fermentation happens much faster during the summer, and much slower in the winter. 

Storing and Using Flake Soil

When the flake soil has aged for the desired time, and looks and smells ready, it’s time to make use of or store it. 

Flake soil will continue to ferment and will lose its nutrition if left to ferment longer than necessary. To avoid this, make sure to dry any finished flake soil that you aren’t planning on using soon. Flake soil that has been completely dried and stored can last up to one year. Be sure to rehydrate the soil before using it to feed beetle larvae. 

When using new flake soil sources, make sure that the beetle larvae have a mix of at least 50% of the old substrate that they were living in before. Putting beetle larvae in 100% new flake soil that they aren’t used to can shock them. 

When maintaining beetle larvae in their containers, sift out the larvae frass (the big poop pellets) and keep the uneaten flake soil to avoid wasting it. The flake soil can be mixed into newer flake soil, and the frass makes great fertiliser/compost for plants. 

Important: If at any point the flake soil smells strongly of wine/vinegar, do not use it for the beetle larvae! It is either too wet, poorly aerated or needs to ferment longer with regular mixing. Beetle larvae can suffocate or suffer from poor nutrition if flake soil is not properly prepared.