Agreed with the above. I've got Lucanus elephus as well, I check them monthly and supplement with koi pellets
I have for raising goliathus. I got mine as L2 in Sept. of 19, one which was an L3, has been an adult female since
August of '20, the others have been eating and are healthy, I use a mix of collected material and flake soil I purchased.
Definitely just tunnels, eventually, they'll pupate, when is anyone's guess.
I'll check mine again in a couple weeks, the one good thing about beetle grubs, is once in an eating environment, they
don't need a lot of care and given the length of time spent as a pupa, and a hibernating adult, you can leave them
be for a long time. When I found my female, it was a surprise, she's been in a small cage for quite some time and
ventures out now and then to eat, One interesting thing, the surface of her substrate has changed to more of a finer
appearance , like it's been chewed up, but she's in there alone..?