Photographs of the cut ends of woody stems. The one on the left has intact interior tissue. The one on the right has a visible tunnel hole at the center.

Figure 5. The stem on the left is not occupied; the pith is undisturbed. The stem on the right is occupied by bees, which have hollowed out the pith and even left a dusting of yellow pollen at the nest entrance.

Photographs of the cut ends of woody stems. The one on the left has intact interior tissue. The one on the right has a visible tunnel hole at the center.

Photo by Elsa Youngsteadt CC BY-NC-SA 4.0