Pretty Galling

This is a gall - an abnormal growth on a plant.

In this case, the gall was caused by a goldenrod gall fly.

The fly deposited an egg on the goldenrod stem in the spring.  Upon hatching the larva ate its way into the stem and set up house there, causing the plant to produce the gall in reaction to the invasion.

With any luck, the larva will eat the living tissue of the goldenrod plant all summer, and then hibernates there for the winter.  Without luck, it might suffer from one of a variety of unpleasant ends.  Wasps sometimes inject their eggs into these galls, and in such a case it does not end well for the larva.  Also, ice fisherman have been known to cut open these woody galls and use the live grub for bait.  Failing that, the larva may become a snack for some enterprising downy woodpecker this winter.

If, however, the goldenrod gall fly larva lives until next spring, it will chew a tunnel out of the center of the gall, stopping short at the last layer of the now brown gall.  The larva will return to the center of the gall to become a pupa, and will eventually emerge as an adult fly, busting through the last outer layer of the gall.

The new fly will live about ten days - long enough to mate - and the process begins all over again.