Hi Housewright,
The adult "emerged" beetles do not eat wood or anything else come to that. Their only purpose at this time in their life cycle is to mate and then die.
During mating the males are required to pass over a packet of nitrogenous nutrients to the females and this is used as the primary source of sustenance for emerging grubs. It is the grubs that eat the wood and they do so for years before they too emerge as adults. Wood is very low in nitrogen content and thus the grubs have to eat their way through quite a few platefulls of wood before they too can metamorphise and exit via "flight" holes as adult beetles. The grubs find it much easier to live and eat the wood after this has been softened up due to fungal action. For fungal action to take hold one needs high humidity i.e. cool damp conditions.
The adult females will weigh any prospective mates climbing onto their back to make sure that he has a sufficiently large nitro packet to transfer to her and any "runts" or "spent" forces will quickly be flicked off.
If one inspects an old chair that has been glued together using animal product (hoof and horn) glue then one can see that the insect damage at the joints is much more significant than elsewhere in the chair. This is due to the high nitrogen content in the glue providing a tastier meal for those prospective beetle studs.
Ken Hume
