Insects emerging from vertical tube
Mud tube, metallic green, bee-like - sounds like a mason bee to me. 

There are several metallic green mason bees (Osmia spp.). As Wikipedia explains: 


  Mason bees are named for their habit of using mud or other “masonry”
  products in constructing their nests, which are made in naturally
  occurring gaps such as between cracks in stones or other small dark
  cavities; when available some species preferentially use hollow stems
  or holes in wood made by wood-boring insects.


One example here:


Photos at http://www.laspilitas.com/insects/megachilidae/osmia-mason-bee.html