These galls are the "packages" left after winter birds pecked through to get at the treats inside.
Last summer, an insect laid eggs at the tip of the plant stem. Each hatched egg became a larva that burrowed into the stem. The larva chewing and its saliva caused the plant to build a gall. This became shelter for the larva as it expected to survive winter and emerge in Spring. However, winter birds often peck the gall to extract the larva. This is one way birds find food in winter.
