Although these wasps are called wood–borers, they will use convenient cavities in any material. When we went out to our summer cottage, in the last days of June, 1895, we found many little wasps of the species Trypoxylon rubrocinctum busily working about a brick smoke–house on the place. Closer examination showed that in the mortar between the bricks were many little openings leading back for a considerable distance, which were occupied by the wasps. It would seem that these holes were excavated by some other agency than the wasps themselves, as they were so much too deep for their purposes that before using them they built a mud partition across the opening about an inch from the outside of the wall. Later we found nests of the same species in the posts which support an upper balcony of the cottage; and here, too, the wasps made use of holes which were already excavated. In the following summer we found large numbers of these wasps at work in a straw–stack. The stack had been cut off perfectly smooth on one side, so that many thousands of the cut ends of the straws were exposed to view, and these proved very attractive to rubrocinctum. This species is very cosmopolitan in its tastes, for we found it utilizing the small holes in the sticks of a woodpile. The straws made the daintiest nesting–places, however, and were well adapted to our purposes, since they could be drawn out of the stack and split lengthwise so that the contents could be easily studied. The two halves could then be brought together again without injuring the inhabitants, and thus we often kept several sets under observation long enough to watch the changes from the egg to the pupa. We found Trypoxylon albopilosum nesting in holes made by beetles in posts and trees, but never in straws. A third species, bidentatum, was very common, nesting in the stems of plants. During the month of August we saw many individuals of this species hunting for spiders on the blackberry bushes; but at this time we were so much absorbed in Crabro stirpicola that we never followed them to their homes.