I Know Everything

My mom thinks I know everything.  Well, maybe not Everything.  But at least everything about nature.  Earlier this month she dragged me over to her friend’s house where she was sure I could tell her the cause of a pile of dried grasses.  I made a guess…  but really… I have no idea.

A couple of days ago, though, she brought me something I did know about.  She brought me this:

The Great Mystery

Mom was pretty sure those were Oak leaves, but she had never seen such weird looking acorns.  “Ha!” says I.  “They aren’t acorns!  They’re galls.”


“Yeah!  And they’re caused by wasps!”

Helloooo! Anybody In There?

“No way.”


One of the many, many, many definitions of gall on Dictionary.com is this one:

Any abnormal vegetable growth or excrescence on plants, caused by various agents, as insects, nematodes, fungi, bacteria, viruses, chemicals, and mechanical injuries.

Galls can be found on a wide variety of plants.  But consider these facts from the University of Florida website on Insect Galls:

  • Of the 2,000+ insects in the U.S. that produce galls, 1,500 are either gnats or wasps.
  • 80% of all gall wasps produce their galls on oak trees.
  • 60% of all known insect galls occur in the oak family.

I found this picture of the wasp that causes the gall at another website.  (Click the picture to go to that website.)

Wasp that causes Oak Apple Gall
Biorhiza pallida: Don’t worry!  This wasp can’t sting you…

Scientists are still figuring out the life cycle of this wasp.  Here’s what they think so far (I think…):  Adult wasps – male and female emerge from the galls in June or July.  They mate and then drop to the ground.  The females burrow down into the ground and lay eggs in the roots of the oak.  Larvae emerge and feed on the oak roots for over a year before pupating.

Oak Apple Gall- Inside

Only wingless females emerge from these underground pupae in early spring and crawl up the trunks of the trees to find new leaves.  They inject eggs (which got fertilized how, exactly???) into the mid-vein of the leaves (unless you read a different website which says they lay their eggs at the base of a leaf bud).  The growth hormones of the insect larvae react with chemicals in the leaf causing the leaf to grow into an apple-shaped gall around the larvae (or larva?  See below).  When these larvae pupate and emerge in June or July, they can be either male or female.

As I said, scientists are still studying this wasp’s complicated life cycle. I found some discrepencies from one website to the next. For example, one said that each gall contains only one larva. Another said that these galls are multi-larval, but that a gall will only contain one gender.  I don’t know about the gender thing, but I did find a gall on the ground one summer and could not resist the tempation to open it, even though I knew that I was probably going to kill the inhabitant…  (Go ahead, slap me!)

Oak Apple Gall- Larva Perhaps
I’m going to have to go with that multi-larval account, based on this picture…

So, the truth is… I don’t know Everything.  And I especially don’t know Everything About Nature.  But then, neither do the scientists…  (Don’t tell my mother, kay?)

Learn more:

8 thoughts on “I Know Everything

  1. Pingback: Festival of the Trees 29: bring out your dead « Via Negativa

  2. Wow! Thank You. I feel vindicated. My husband swore they were acorns that formed at certain intervals in an oak’s growth (say every so many years). I do not recall how I came to be sure that these contained these critters (maybe my brief stint with 4-H in the 1970’s) but I was certain…again Many Thanks!

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