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Sunday, May 31, 2009

Oak galls

This is a short article about Oak tree galls. These form on the limbs of valley oak trees. They are the result of a tiny wasp laying its eggs under the bark of the trees limb. The tree forms this tumor like growth which makes the perfect home for the wasp larvae. It doesn't hurt the tree. I have seen trees covered with hundreds and hundreds of these in all sizes. This one is 2 1/2" in diameter and the average size. You can almost see the holes at the top right. This is where the wasp emerged from the gall after maturity.

.This is what the interior of the gall looks like. In the center is the chamber where the larva lived and you can see its tunnel to escape to the surface.

Heres what the galls look like on a valley oak tree.

Heres a photo of the wasp. The name of the gall wasp is Andricus californicus. Its less than an 8th of an inch long.

These galls are supposedly an excellent tinder and will catch and hold a spark from flint and steel or a ferro cerrium spark rod, AKA fire steel. These and other types of galls were used to make ink and for dyeing. They all have a high tannin content. In ink the tannin is used to react with ferrous sulphate and makes a black fluid. However after a long time the acid in this ink will eat the paper. Thats why some old documents are damaged. The tanning process also uses tannin and these galls would work for that purpose.

6 comments: said...

Of all the gall!

I have always wondered if these galls were harmful to the tree. The galls I see on oaks are always green, just like the leaves, and so are likely still doing photosystesis.

I assume the firesteel will only light dry galls.

Ron Layton said...

Yep. The dry ones are used to catch sparks.

Diet Plan said...

Very interesting blog with nice pictures I like your blog... :).

Anonymous said...

Where can I get a pail full of these? I would be glad to pay a little for some to play with...

Anonymous said...

Monastic ink: linking chemistry and history

About the science, art and history of gall based ink.

Ron Layton said...

ddshutt, if you are still around, get hold of me and I'll get you as many as you want.