They are brown mites, and they are generally not a problem in a worm bin. They are not a threat to worms as predators and unless you have thousands of them, they are not really going to compete with the worms for the food. They are usually an indication that the bin is too wet and too acidic. In you picture, it looks like there is excessive moisture on the plastic lid. Try to drain more water out of the food you are giving them. A good way to do this is to mix their food in a blender into a pulp and then let it sit in a strainer so water will drip out of it. I have found even a better way to remove excessive moisture is to freeze the food pulp. Once frozen, you then can pop it out of the container onto a plate and let it totally defrost. You will be amazed at how much water comes out of it. (Freezing their food also has the benefit of killing off any fruit fly eggs.) For acidity, add some calcium carbonate to raise the pH level. Best to invest in an inexpensive combo moisture/pH meter so you can try to attain the "norms" that your worms will do the best in.
He was expelled for perverse baking experiments. This tiny ad is a model student: