Did anyone try rearing them in myceliated subs? I know Pleurotus sp (oyster mushrooms and related species) generally work fine for many Dorcus larvae and a few of the larger Prosopocoilus species' (eg confucius & giraffa) and Trametes sp. (turkeytail mushrooms and related species) and Ganoderma sp. mycelium work okay for Mesotopus and Allotopus larvae. Most people know of mycelium as being good for rearing larger beetles, but in my experience most larvae grown under the right temperature conditions for the larvae AND the mycelium tend to grow faster than those raised under normal semi-fermented substrates used for rearing Lucanidae larvae under similar temperature environments. Perhaps there's a good matching mycelium species for L. elaphus?