Crickets left in the cage overnight can attack and injury a sleeping dragon. Many crickets will bite around eyes, looking for moisture, nibble on any exposed areas and over time cause sores that can become infected and eventually lead to the death of your dragon. Normally this won't happen over night, unless you have a large amount of crickets in the cage over night.
For small crickets, i find it is best to just put them in a ceramic bowl with sides high enough for the crickets not to be able to jump out but low enough for your dragon to get over to reach the crickets. A 6wk old dragon should be able to eat 1/4" crickets, which are not too hard to pick up.
When I remove uneaten crickets, I just use my hands but my crickets are big enough to easily pick up or scoop out with my fingers. Smaller crickets are probably easier to just squish against the paper towel and left till cage is cleaned the following day. I typically do the cricket cleaning about an hour after lights out, this way the dragon is asleep and less likely to get panicky or stressed...she does wake up and watch me but takes to real objection to my arms moving around her sleeping area. Also, at night the crickets come out of hiding so you can see if there are any around. I also pat down all over the paper towel substrate for the crickets hiding underneath or within folds.
If you are not sure if crickets are still in the cage, leaving some fresh chopped greens in the cage over night will solve the problem of the crickets eating your dragon. They prefer the fresh greens as both a water and food source.
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PHLdyPayne