If you use Repti-Bark (or any fir chips/bark) for bedding, it can sometimes come pre-loaded with harmless little critters known as book lice or bark lice. We found them in our royal's cage one time. Our daughter used her digital microscope and a encyclopedic animal book to identify what the critters were. We then took a micro digital image and had an entomologist confirm that she was correct. Kids are awesome! Anyway, they're very, very small, white/light colored things. They can also occur if your cage is too moist, developing mold, which is their food of choice. Perhaps that's all it is? If so just clean and sanatize everything to the max!

As a side note... now I always freeze my bark for 24 hours, killing any bugs, before introducing it as bedding.

<EDIT>
Here's an image to help identify Psocids (Book Lice)
http://sgrl.csiro.au/storage/insects...s/psocids.html