Vermicomposting, worm bin, composting with worms community and forums
"Arching" or "bridging" is fairly common on narrow flow throughs. I just bought an 18" icing spatula to run along the sides as described by Daniel - I'll let you know how it works next time. In the past, I would just break the bridge by inserting a small dull blade or trowel in the middle of the bridge area, and when you pull it a bit and take it out, a small cave-in results. Better than an avalanche and minimizes casualties.