My Bearded dragon, Jaegar keeps opening his mouth when we try to handle him. He is only 4 months and sometimes he’s fine and doesn’t open his mouth, but this morning he did it to me and my wife. Anyone knows why he would be doing this?
Did you try and get him from a different angle than usual? Is he nearing a shed? What bulbs are you using in that fixture? What are you using for bedding? Young dragons do best on carpet, tile, non adhesive shelf liner, and a few other solid substrates. Older dragons, since they're less at risk, can be housed on sand but is generally still advised against since an adult dragon can also be impacted if he or she ingest a lot of sand. If your dragon is on walnut shells or sand, it'd be best to use some of the substrates listed earlier.
I Believe you are scaring him. He is in a defensive position because you are gigantic to him and he thinks you're a predator and will eat him. You aren't of course but its his instinct to stay alive. I Would try to go to him very slowly and maybe let your hand just rest in his cage. Eventually he will get to know that you're not a threat and lighten up to you.
Some other good substrates are: Paper towel, newsprint, slate tile, peel and stick tile, or Even linoleum will work. Just don't ever have Any age beardie on ANY type of loose substrate.