Saturday, July 14, 2012

Pip Galls = Pandemonium in the Pin Oak

Recently there has been a small uproar in the Pin Oak over some honeydew-exuding pip galls.
   The yellow-jackets and ants have been all in a frenzy over the glistening globules of honeydew oozing from the tiny galls.  I'm pleased to have this drama playing out in our backyard.  As you can tell, I too, am going to make a fuss over these oak galls, because what is happening within (and without) those galls is profound!
   In my opinion, the picture of the honeydew droplets on the acorn pip gall (above) represents one of the most amazing things I've posted about so far in all 200 of my Nature Posts.
   Think about it... a wasp larva hidden inside this small gall has caused the oak tree to grow the gall to feed and shelter the larva.  Not only that, but the gall-maker also causes the gall to ooze honeydew which attracts yellowjackets and ants.  These in turn, protect the gall as a food source, and in doing so, are unwittingly protecting the gall's inhabitant from parasitic insects.
 The fact that these wasp larvae can cause their oak galls to ooze honeydew is, I think, the most incredible thing about these pip galls.

Now, it is amazing how the Cynipid gall wasp larva causes its host plant to grow a structure that houses it and also feeds it,

but, hey, gall-makers do that kind of stuff all the time.

   What this larva is programed to do is bordering on awesome.... the wasp larva can cause its host oak tree to turn the larva's larder/shelter into something like the nectary of a flower whose job is attracting guards (protectors) instead of pollinators.  Profound!

 Check out the photo below and you'll see what I mean.  Who would argue with this guy... when you can see it claims the gall... and says, "It's mine.. all mine... and if you stick that big thing any closer... I'll..."
Ants slip in for a sip of the honeydew when they get a chance.
Ants are protective of their honeydew sources as well.  I didn't try this with the ants on the pip galls, but with ants milking honeydew from aphids, a finger placed nearby will soon be covered with agitated, biting ants.
 Our Pin oak was bustling with prowling yellowjackets and scurrying ants hunting for the honeydew droplets.
  Pin Oak's lower branches characteristically droop, so as I walked past, these amazing galls were right at eye level and easy to observe.  Finding information on the galls wasn't quite as easy.  I found little written about these acorn galls.
I did find, on page 100 of Lewis Hart Weld's Cynipid Galls Of Eastern United States, a brief description of the acorn pip gall of Callirhytis balanacea.  These galls seem to be a match....
They are small, round, green galls which grow on the stems beside (or out of) the young acorns.  They secrete honeydew.  They drop off the Pin Oak tree in late June.
   Over the time I was taking the photos of the galls and the honeydew seekers, I noticed that the galls were disappearing.  Since the pip galls drop off when they mature... and because I wanted to confirm in my mind that there were many more galls up higher in the Pin Oak tree... I laid a small tarp under a portion of the Pin Oak in order to catch the dropped galls.
About a dozen of the detached galls landed on the tarp over the period of two or three days.  Then the galls quit dropping.  The dropped galls quickly turned black.  I guess the pip party's over for this year.

   Ahhh, if only honeydew galls were really big (I'm thinking big enough for a good human-sized sip of honeydew) and there were always lots of them!  Well, a moderate amount of them... we need acorns as well.

Maybe I just wish... that there would always be some pip galls in the pin oak.

BTW... I doubt many people purposefully search the web for acorn pip galls.  Perhaps you, my regular readers, would pass this post along (via email, etc) to some folks you know who would enjoy these pictures of yellowjacket-protected pip galls.  Wouldn't it be great to perpetrate some online pandemonium over pip galls in the pin oak?


  1. I shared your post with Amy-Lynn who has a nature blog called "Flandrum Hill". I know she'll enjoy it.

    As always -- a fascinating post.

  2. Did you tried to taste the honeydew ?

    1. Wong,
      I didn't try tasting the honeydew. I have tasted nectar from flowers and I assume it would taste similar. I've read that honeydew does not taste sweet, but I doubt that information since honeydew is mostly sugars. Here is a link to a report about Native Americans gathering aphid honeydew. The author described the taste of the honeydew as "very sweet" but with a "disagreeable flavor".

  3. Somehow this post really piqued my interest. I think your blog writing skills are improving!

    1. Luke,
      I'm glad to hear that!
      My writing skills still have lots of room for improvement... for that matter, I can't even type. I reckon that's one reason I try to let my pictures do most of the talking :-)