Periodically when I go to add scraps to my outdoor compost bin, I notice that there are worms gathered around the outer edge of my bin, under the lid. There are others in various areas on the inner rim of both the bin and the lid, and I can't tell if they are trying to get away or if they are headed inside. I was just wondering if there was a specific reason why the worms do this and if it is because they don't like the conditions, if there is something I can do to help prevent their leaving?
I've been vermicomposting for more than 25 years and what you describe is just normal earthworm behavior. I, too, have often wondered what they mean by it, but have never come to any kind of conclusion.
Do you ever provide something besides food waste? Old autumn leaves? Straw? Shredded office paper? Worms especially seem to benefit from a portion of leaves now and again. By "benefit" I mean, increased castings production and a burst of egg laying. I don't have any scientific evidence of that, but it's been my observation.
I suspect you are doing everything just right. Tweak with a little carbon source (leaves, straw, paper), and carry on!