Friday, June 6, 2014

Photographs Of The Life of a Pitch Nodule Maker

   Four months ago, on a cold January day, I turned aside from the trail to see if there was anything interesting in some Scotch Pine trees.... Of course there was!  There were some lumps of pitch (pitch nodules or pitch blisters) on those Scotch Pine branches.  I pried open a pitch mass and there was a Pitch Twig Moth larva looking very alive and well.  Right then and there I decided to see if I could rear some larvae to adulthood so I could photograph the whole story of the pitch nodules.
Here is a photo of a Pitch Twig Moth, or Pitch Nodule Moth (Retinia sp.), which I reared from one of those lumps of pitch.
A Pitch Twig Moth, or Pitch Nodule Moth (Retinia sp.)
Now for the story of the life of a pitch nodule maker.
pitch nodule of Pitch Twig moth larva
   When the pitch nodule moth larvae were young, they tunneled into twigs on the Scotch Pine.  The caterpillars managed to keep the pine's pitch flowing and used it to form the masses of pitch over their tunnels.  The Pitch Twig Moth larvae fed on the interior of the twigs, and it would seem to me, some of the resin.
  It would seem that living hidden in this resinous mass affords the larvae some protection from predators.
pitch blister of pitch nodule maker
   The moths have a two year life cycle and that is evident in the photo below... the older pitch has a darker look and notice that the twig is swollen, or deformed, opposite (under) the pitch blister.
pitch nodule on Scotch Pine twig
The pitch nodule maker in the photo above probably hatched from its egg mid-summer two summers ago and started chewing into the wood at the branch junction on the upper right of the pitch nodule.
   In the photo below, I pulled back the pitch mass to reveal a caterpillar.  The pitch nodule maker is in its 'ditch' on the left side of the picture.  Notice the silk webbing between the caterpillar and the pitch in the foreground - the caterpillar must use silk to manage the sticky, oozing pitch.
pitch nodule moth larva in pitch nodule
Yes, I can imagine you can almost smell the pine pitch.  I imagine it's a sticky situation inside that pitch blister.  Notice how the channel it excavated in the twig is covered with pitch.
cross-section of pitch nodule

The inside of the pitch nodule is made up of minute balls of pitch and frass.
frass in pitch nodule

I found that the larvae had begun to pupate around mid May.
pupa of Pitch Twig Moth (Retinia sp.)

   About a day or so before the moths emerged from their pupae, each pupa wiggled completely out of the pitch mass and dropped to the ground.  At least that's what they did in my rearing containers. Perhaps in the wild they wiggle out only part way before the moth emerges.  Anyway, a couple of weeks after pupating the adult moths emerged from the pitch blisters.
Here is a photo of a Pitch Twig Moth at home on the tip of a pine needle.
 Pitch Twig Moth, or Pitch Nodule Moth (Retinia sp.)

Soooo, there you have it.... the story of the pitch nodules I found when I turned aside from the trail on a cold January day.
   Actually, there might be a bit more to the story.  I noticed some small orange things on the surface of some of the pitch nodules.  Right then and there I decided to see if I could figure out what they are. My first thought is that those look like fruiting bodies of a fungus that grows in the pitch.
surface of pitch nodule
How about that?  Could it be, that, if there is fungal growth in the pitch, that it is a symbiotic fungus or is it simply incidental?  Whatever those orange things are, I would like to find out.
It seems there is always more to the story than meets the eye....


  1. I work on a Christmas Tree Farm in Battle Creek, Michigan and I discovered several of these things. I did not know what they were and contacted a person working at the Forest Services Division who sent me a link to this. Thank you. They were on the Scotch Pines. Most were on the leaders of the young trees.

    1. Lindsay,
      Glad to help you "see" and understand what goes on in those lumps of pitch on your Christmas Trees.

  2. Fascinating post as always Dana.

    1. Thanks Sybil. I had fun watching the Pitch Nodule Moth's life cycle.