Why isn't my rainbow stag beetle eating??

[Scarabs]

My rainbow stag beetle doesn't seem to be eating and I want to know why. I also want to know how to get him to eat

 

[JKim]

It looks like you are keeping an adult pair. It could be because they are a fresh adult pair (takes little bit of time until becoming mature enough to actually start active or feeding), temperature is not warm enough for them (anywhere below 70 usually makes them inactive or even hibernate), Provided food is just not attractive. (If you are providing jellies from Titan's, then that might not be the case).