Monday, October 08, 2007

Fuzzy growth on underside of oak leaves

Every year about this time in autumn, I find a lot of mysterious little fuzzy peach colored balls on the ground under our oak tree. A few days ago I pruned an oak branch which was shading too many understory plants and I finally found out where those balls come from. There were a number of those fuzzy things attached to the undersides of the leaves.

I detached a fuzz ball which resembles the fuzz on tennis balls and could feel a hard kernel inside so I pulled off the fuzzy material and saw a green seed like object. Initially I thought it was a seed of some kind of parasitic plant but how a plant could attach itself to the host plant leaf was a mystery especially when the branches were several feet off the ground and I didn't see any vine like plants climbing the tree trunk. I thought it could be an airborne seed but how it would find a specific host was problematic.

I did a quick online search for oak galls and came upon some images that resemble the ones I took. Apparently it is the pupa of a wasp that lives in the gall! And the "seed" is not a seed at all. The gall is called a woolly oak leaf gall and the inhabitant is a parasitic gall wasp belonging to the genus Callirhytis. And here I was all set to plant the 'seed' to see what came up. ;)

I'm glad I solved the mystery of the fuzz balls which has been nagging me for about 3 years. I guess I should cut open a gall to see if I can find the pupa inside.

Here's an image of the Callirhytis wasp though this may not be the specific one that creates the woolly gall. And here are more photos of oak galls including the woolly oak gall.


Blogger Annie in Austin said...

Very interesting Ki, and at least it isn't anything you have to treat or do anything about!

I've seen other kinds of hard-type oak galls, but yours is really different... sort of looks like the blown-up drawings of cells dividing in old schoolbooks.

Annie at the Transplantable Rose

9:11 PM  
Blogger Ki said...

Now that you mention it Annie, the gall does look like cells dividing. Interesting that the wasp would lay several eggs in a cluster and that each egg would induce the oak to produce the fuzzy protection around it. I'm glad it's not a huge pest.

I've seen the hard galls too but these are quite small about the size of a large green pea and I haven't seen any larger than a chick pea.

4:37 AM  
Blogger mugsiekay said...

help..I have I need to worry about these galls hatching? I would have millions of wasps if so....what do I do?

9:24 AM  
Blogger mugsiekay said...

will these guys turn into wasps??/ am I gonna have to worry about tons of wasps?

11:11 AM  
Anonymous Anonymous said...

Hey i see that in school theres lots of them growing on the trees theres alot of them im gonna show my friend this link cause we always look at these fuzz balls

9:23 PM  

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