Saturday the wren continued to enter the porch and I had to open the porch door to get it out.
Sunday morning I watched it outside the screen near the floor of the porch. It then flew up to one of the upper beams and before long it was in. Again!
Dan got out the step ladder Sunday afternoon to see if he could find the spot where the wren was coming in. At the highest point which he reached only by stepping on to the horizontal beams he was rewarded for his effort by discovering a small gap in the netting. The wren could push its way in at that point but not go back out. Dan took a rag and stuffed it in the hole. No wren since then, thank goodness!