Kinshi (Made With Lions Mane Mushroom)

In Japan, stag beetle larvae are grown on in a bottle. Kinshi is the Japanese word for mycelium, and a kinshi bottle is hardwood sawdust run through by a white-rot fungus until the block holds more fungal tissue than timber. The larva burrowing through it is feeding on the fungus first and the softened wood second, which is the part most descriptions of this material get backwards.

That distinction has been tested. Larvae have been reared successfully on artificial diets made of fungal tissue and nothing else, and when researchers split freeze-dried mycelium into its soluble and insoluble fractions, each improved growth against the control, though neither alone matched whole mycelium. Beetle grubs cannot break down lignin themselves. Adult female stag beetles carry pockets called mycangia, found in the females of every one of twenty-two lucanid species examined, and the five that were cultured held xylose-fermenting yeasts, which the females seed into the wood at laying. Left to a white-rot fungus, lignin and cellulose both come apart, which is what turns indigestible timber into food.

Two things to be straight about

Lion's mane, Hericium erinaceus, is a white-rot fungus of beech and oak, so the mechanism above holds for it. It is not one of the species Japanese breeders traditionally use, which are the oyster mushrooms and turkey tail, so treat this as the same mechanism by a different fungus. Second, and more practically, this material is supplied dried and a kinshi bottle never is. The Japanese product is a live, refrigerated block with a shelf life measured in months, and the larvae are reared inside it. This is a food you add, not a medium you rear in, and any listing that tells you otherwise about dried material is overselling it. Drying does not spend it, because the fungal protein is still there and the freeze-dried work above shows dead mycelium still feeds larvae. What is gone is the living, spreading culture.

For larvae, rehydrate until it holds together when squeezed without dripping, and work it into the rearing substrate or lay it on the surface where they will find it, refreshing as it goes. For wood-eating isopods and millipedes, break it into pieces and mix it through or scatter it over the surface, then leave them to work at it in their own time. It pairs naturally with flake soil and shredded rotten wood, which are doing a similar job by a different route.

Keep the unused portion dry and sealed and it will not spoil. If you are setting up for beetle larvae from scratch, the rainbow stag beetle larvae listing covers what they need alongside this, and the rest of the substrate range is in accessories.