Naturespeak A naturalist's view of the world

January 20, 2008

Annuder Gall?

Filed under: Uncategorized — wykes @ 9:11 pm

  Yes, just when you thought it was safe, I have the outright gall to present you with yet another type of goldenrod gall. I’ve already directed your gaze to the likes of the Goldenrod Bunch Gall and the Goldenrod Ball Gall. You may recall that these structures are essentially plant growths caused by the activities of an insect. Goldenrods, those yellow fall flowering field flowers (say that three times in a row) are host to a wide variety of gall creating insects. Those first two, one of which caused a ball shaped swelling and the other a bunched-up cluster of stunted leaves, were members of the fly clan.  The new gall in question is called an Elliptical Goldenrod Gall and it is the work of a tiny moth.

  As you might have suspected, the Elliptical Goldenrod Gall is an elliptically shaped gall found on the stem of goldenrods.  Another shape-related name for this thing is the Spindle Gall, but if you don’t know what a spindle is this is of little help (this is a wool spindle).  Insects are usually very particular about their plant hosts and the elliptical gall maker deliberately selects Canada, Late, and Giant Goldenrods.

  You’ll note that there is a hole located at the very top of the swelling (if you didn’t, look again). This hole is a key feature in understanding this gall and its creator.  The moth responsible for the whole affair is a tiny thing with the incredible scientific name of Gnorimoscherma gallaesolidaginis (say that one times fast and you are doing good). The common, and pronounceable, name of this insect is the Goldenrod Gall Maker Moth.  Like all moths, it starts as an egg which hatches out as a larva.  The larva, a.k.a. caterpillar, crawls up the stem and burrows in. This incites the stem to swell and entomb the happy little caterpillar which blissfully eats away at the nutritious walls of its cell. About mid July, the fat sassy ‘pillar has had enough and is ready to become a moth. Before pupating, it chews a tunnel up through the gall wall and promptly fills it with silk and debris. Then it retreats back into the chamber and converts into a pupa. This last step is especially important because the adult moth has no chewing mouth parts so would be unable to get out of the gall once it emerged from the pupa.

  It takes about a month before the adult moth emerges from its pupal skin, forces it’s way up through the silk blocked tunnel, and punches though the opening. If you’ve been keeping up with the chronology of this life cycle, you’ll correctly figure that the adults come out in late September.  They lay their eggs in the leaf litter and die long before the gales of November bring in the cold season. This logically means that those elliptical galls, like the one pictured, are actually empty by the time you find them in mid-winter. Logic can only go so far in the world of nature, however.

  If you chose to investigate you will find that many of the elliptical galls will contain life in January. The life form within will not be the original occupant, however.  It is a stark fact of life that such inconsequential beasts as gall moths have even more inconsequentialer life forms that take advantage of them. There are at least four parasitic wasps that can lay their eggs in the moth caterpillar and develop inside the larvae’s body.  They eventually kill their host and complete their development on their own time – often staying throughout the winter.

  Whether a moth or a murderous stranger emerges from the hole atop the gall has already been settled by the time the snow flies.  Most of the time it is a moth that exits the port and the gall sits empty.  Those other times are not galling or appalling, but simply nature’s calling.

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