The Incredible Emergence of the Wool Sower Gall Wasp

In early May, I went hiking and found a cottony gall on a white oak sapling.  The kid in me was immediately awake and excited, because I knew that something was inside that gall and changing into an adult insect.  I was the kind of kid and am the kind of adult who likes to raise caterpillars and other larvae to watch how they metamorphose.  But, this I had never seen– never had the opportunity to see.

What is a gall?, you might ask.  Galls are any outgrowth on the surface of a living organism, often caused by a parasite, disease, or genetic mutation, and on plants alone, they can range in form from aesthetically pleasing to disgusting.  Oaks are susceptible to a variety of galls, and if you’ve been hiking around an oak forest in the fall, it’s not uncommon to find papery brown balls on the forest floor  called oak-apple galls.  These galls are caused by a wasp that lays its eggs in the oak’s living tissue, as are many oak galls.  So, I suspected that the gall I had found was also caused by a wasp.  I had never seen these wasps.  What would one be like?  What would their emergence be like?  The suspense was killing me.

So, I took the branch with the gall home and plonked it in a jar of water.  Now, before you call me crazy for wanting to raise baby wasps, let me clarify one important point:  Most wasps do not sting.  That’s right, the word wasp generally causes incredible hype, because, let’s face it, wasps that sting are much more memorable than wasps that do not sting.  Wasps that sting (i.e., paper wasps, yellowjackets, and bald-faced hornets), if disturbed, will chase you down with their keen eyesight, and poke their stinger into your skin injecting painful venom.  We are not talking about those wasps.  Most wasps do not sting.

Also, these particular oak gall wasps are parasitic — they depend on another organism, an oak, to grow to maturity and to lay eggs.  And, if you haven’t noticed on this blog yet, I have a particular affinity to diseases and parasites, mostly because they are elusive, complicated to understand, often beautiful and horrifying at the same time, and tricky beasts to study.

Gall on white oak

Well, I waited and waited, and eventually the oak leaves wilted and nothing seemed to happen.  When I was cleaning the house at the end of May, I decided that it was time to clean up the wilted oak branch on the windowsill with the big cottony ball stuck on it.  The big, cottony ball was turning brown, and I thought maybe it was dying.  Before throwing it out, I decided to open it up to see what had been in there.

And, lo!  Inside the cottony mass were hard, tan pods the size of rice grains.  Some of them had a hole punctured in the side, indicating some of these pods had hatched something (How could I not have noticed wasps flying around my house, I thought incredulously).

Inside the oak gall

Some of them had not hatched, and the geek nerd kid inside me woke up and told me to use my pocket knife and see what was inside.  I gently pried one open… and pulled out a tiny, ant-sized adult wasp.  More wasps were emerging and crawling around the porch floor.  I was giddy with this unexpected discovery.  I had never seen a wasp like this before!

Wool Sower Gall Wasp

I have now identified my wasp as the wool sower gall wasp.  Like many oak gall wasps, it doesn’t cause major damage nor pose a major threat to the trees on which they grow.  Parasitic wasps are often very specific to their hosts, and have co-evolved all sorts of weird traits in response to their hosts, such as amazingly and creepily changing their host’s growth, behavior (if it’s another animal), and tissue.  Incredible.




The Incredible Emergence of the Wool Sower Gall Wasp — 2 Comments

  1. I found a lot of these images on our oak trees. Not knowing if we had white or red oak, since it had already been 13 years in the growing. But my concern is that the leaves are brown on the end and green inner of the leaf. Will this evently kill the tree and surrounding trees?

  2. A friend just sent this to me I have ten beautiful white with pinkish dots on them on my oak tree – wow

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