Sunday, November 8, 2015

It's Leaf Kicking Weather

October 26, 2015:  Mildred Knaipe County Park

Wild turkeys enjoying leaf kicking weather
It’s leaf-kicking time – one of my favorite times of year.  Often Oregon’s rains come before good leaf kicking.  This year we’ve had enough rain to dampen the fire hazard but its still dry enough for a layer of crunch leaves on the ground and more falling.  Big leaf maples seem to fall whenever the mood strikes, even on warm, still days.  Other trees require a good shaking by the wind.  Even pine trees join the act, dropping old needles, but hanging on to the majority of needles.  I used to wonder when pine needles dropped.  I can tell you it’s right now.  Patches of sidewalk near my home have turned burnt sienna with fallen needles.

Dale and I have been walking a trail on the Mildred Knaipe Ranch, a county park near us.  It’s late afternoon.  Shadows are long, the ground is damp and the air mellow.  A few late dragonflies still buzz over the pond.  I spooked a honey bee a moment ago.  Not much left for them to gather nectar from, but they seem to enjoy mushy apples scattered on the ground.

The trail takes us into oak woods – big white oaks.  They must have been well established when Mildred first took over the ranch from her father seventy-five years ago.  I start leaf kicking.  There is still a streak of little girl in me. 
Pretty soon I notice some of the oak leaves have ping pong ball sized galls on them.  Any I find on the ground in the summer time are crisp and crunch when I step on them -- obviously left over from the year before.  These catch my attention because they are a little rubbery and have some weight.  They aren’t left-overs.

I’ve been curious about these galls for a long time.  A few grow on oak leaves right along my driveway, but I never see any insect activity around them.  I know they develop when some kind of a gall wasp lays its egg on an oak leaf. I keep hoping to see a wasp either emerging or laying an egg. 
Speckled Gall Wasp

This is next best.  There actually is a fully developed, humped-backed wasp inside the first gall I pop open.  It's tiny, less than 1/4 inch long.  Its wings look a little crumpled when I first break open the gall, but the wasp soon shakes them out and they look usable.  We hurry to take  photographs before it flies off.

Lots of galls on the ground.  I think I could easily collect two dozen.    I pop open four more.  One is empty, two have fairly large white grubs in them and one has a hard knot in the center – with a tiny grub inside. 
When I get home and look for information, I realize we’ve stumbled upon another of nature’s amazing stories.  Bug Guide verifies our little insect is a wasp, a speckled gall wasp (Cynips mirabilis).  
The wasp's pupa was inside the cavity in the center of the gall.
Last spring a speckled gall wasp laid an egg in the oak leaf, triggering the formation of the gall and a home for the tiny grub.  The hairs radiating out from the center indicate all is well with this gall.  If you look carefully you can see the center is broken open, releasing the wasp. 
I look for more information on the internet ….. and this is where it gets really weird.  Back in 1930 a gentleman made a careful study of gall wasps -- Alfred Charles Kinsey.  Yes!  That Kinsey, the one famous for his later studies on human sexuality.  I never knew he started with bugs!
According to Kinsey the speckled gall wasp has two very different generations.  The galls I’m finding now are the result of an agamic female female laying her egg in a fresh oak leaf last spring.  ‘Agamic’ means she didn’t need a male in order to reproduce.  The adults that emerge from these galls usually emerge in late fall and into the winter.  This generation has both males and females.  Once fertilized these females lay their eggs in the scales of unopened buds.  They’ll develop into agamic females in time for the spring egg laying on fresh oak leaves.  So every year this little wasp has two generations, one as a result of sexual reproduction and one an agamic generation. 
If you look carefully you can see a grub, probably a moth larva, that is nearly as wide as my fingernail.

Bug Guide also let me know the large grubs I found in two galls aren’t gall wasps grubs.  Another insect has taken over the gall, probably a moth.  The wasp’s gall has become the safe haven for this intruder. It has even been suggested by the kind gentleman who commented on my grub that it would be nice if I try to raise some of these grubs and see what kind of moth comes out.  
Hmmmmmm…. I just might. 
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P.S.  Nov 6:  We went back to the park and collected a couple of dozen galls.  My plan is to keep them in a damp terrarium on my deck, wire screen on top, and wait and see if any moths emerge. 


  1. Great information- I will stay tuned for your results:-)

  2. Every year my oak tree gets these oak galls. I find them fascinating. Thanks for all the info on them. I'll be excited to see if anything emerges from yours.

  3. Maybe just enough info to turn my attention from killing invasive buckthorn and pics of fungi to oak leaf galls. If you can raise a brood of spiders on your back porch, I'm sure you'll get a gall wasp also. Surprising that the gall can be taken over by another insect. Evolution leaves no opportunity un-tested.

  4. Leave it to you to reveal the hidden insect secrets of an oak leaf gall. Look forward to hearing of your results with your specimens.