Friday, December 7, 2012

Wormy Acorns With Silk-curtained Windows

   Here and there among the fallen acorns scattered on the forest floor you'll find a few acorns with sealed holes - acorn windows... at least that's what I call them.  These windows are spun of silk by the caterpillars of Acorn Moths.  They cover holes made by other acorn insects.
acorn with sealed hole
Acorns with silk-curtained windows.... hmmm, very curious.
   I've already posted about what made the holes in these acorns, so now let's take a real close look at sealed holes and then the caterpillar that made the windows.
acorn with sealed hole
Notice how the "window" looks like some kind of membrane, or plastic, covering the pin-head sized hole.  You'll see later that the seal is many layers of of fine silk webbing.
acorn moth caterpillar's sealed hole
There seems to be an additional substance coating the silk webbing... perhaps wax that acts as waterproofing.  I launched a half of an acorn shell which has a sealed hole in the bottom... as you can see the seal lets no water in.  The acorn boat has not taken on water for an hour or two. 

   I don't know that the function of the seal is to keep out water... I suspect that the main purpose is to keep out unwanted guests.  There are plenty of other insects that will invade an acorn, so perhaps the window encourages them to seek out other acorns 
   This photo shows a microscopic view of the material that was used to cover the hole in the acorn.  I used oblique lighting to highlight the silk strands that seem to trend in one general direction - perhaps one layer?
Actually there are many criss-crossing layers of silk strands...see this next photo of a microscopic view (at very high magnification) looking at the silk window.  acorn moth caterpillar silk window
The Acorn Moth caterpillar's job of spinning its curtains looks similar to what paper or cloth looks like under the microscope.
Here is another photo of the Acorn Moth caterpillar's silk creation... taken with oblique lighting to accentuate the layering.acorn moth caterpillar silk window
   In our experience, this time of year the acorns with the sealed holes were occupied by a small, white caterpillar - the larva of the Acorn Moth, Blastobasis glandulella.  Here is a photo of a cut-away of an acorn showing the Acorn Moth caterpillar on its frass pile inside the acorn.
acorn moth caterpillar, Blastobasis glandulella in acorn

Here is a photo of the Acorn Moth caterpillar.
acorn moth caterpillar, Blastobasis glandulella
Acorn Moth Caterpillar

Here is another photo of the Acorn Moth caterpillar - one that refused to stay on its feet for the picture.
Acorn Moth caterpillar, Blastobasis glandulella

   This photo shows a cut open wormy acorn.  The Acorn Moth caterpillar is visible near the top center of the acorn... it is partially sticking out of one of its tunnels.
wormy acorn with Acorn Moth caterpillar
Notice the caterpillars tunnels in the acorn as well as the webbed frass pile.
wormy acorn
   I suppose the caterpillar does its best to keep a tidy house there inside of its little capsule.  This is probably going to be its home this winter and until it turns into a moth, so why not?  Oh, and how did the caterpillar get inside this acorn in the first place?  Remember that this hole was made by an exiting acorn weevil?  Later, an Acorn Moth layed an egg in the hole and, well, soon enough there was a wormy acorn with silk curtains.
Acorn Moth caterpillar's silk seal
The round window reminds my son of a window in a Hobbit hole...  reminds me of a port hole.
All seriousness aside, let your imagination drift through the oak forest at twilight...
Its fall, and the forest floor is blanketed with leaves and peppered with many fallen acorns.  Many of those nuts have tiny, silk-curtained windows.  I like to imagine the acorn dwellers turning on lights inside their snug abodes.
a silk acorn window
Well, aren't well-lit windows rather appealing during a cold, darkening evening?   Too bad they can't leave a light on for us.

1 comment:

  1. You are giving us some amazing images with your new camera, AND a microscope ! Wow. The macro of the "curtain" is quite lovely. That last shot with the lights on in the little acorn house is fun.