input: [It might be...] mites. Bummer. You can choose one of two treatments: do-it-yourself, or get help from the vet. (1) To do it yourself, you'll need to get small animal mite spray from the pet store. Then follow the instructions on the AGS Care Page for Mites. Or, (2) your vet can prescribe Ivermectin, which you will dose orally; it will destroy the mites. In either case you should plan to clean gerbil tanks frequently. [My Gerbil...] 
output: has bugs crawling on him!