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Urban species #261: Oak apple gall wasp Amphibolips confluenta

Acorns aren't the only round objects falling from oak trees this time of year. Spheres, about the size of golf balls or slightly smaller, green and mottled with red, mysteriously appear on the sidewalk. Later, many more will be found--larger, light brown like dead leaves, sometimes entire, more often with a single hole in the thin crust. These mysterious objects are not pods from outer space, or oak tumors; they are galls: the protective nurseries for young insects, usually given the quaint name "oak apples." The mother insect enlists the help of oak trees, symbolic of strength and live itself, to shelter her growing offspring. Known, somewhat anticlimactically, as the oak gall wasp, the tiny non-stinging insect deposits her egg in the flesh of an oak leaf. Along with the egg is a hormone that induces the oak tree to form a gall around the wasp egg. The larva develops within a shield of plant material, a capsule suspended in the center of the orb.

At least 200 species of organisms use oak trees to form galls of one kind or another. Other plants that often play host to gall wasps and gall mites and other creatures include goldenrods, maples, and roses. Galls cause very little damage to the host plant, and gall wasps are not considered to be serious pests.

The gall is not an impregnable fortress, and many predators recognize wasp galls as sources of food. Birds, notably woodpeckers and chickadees, poke holes in galls when they encounter them aloft. Fallen galls are fair game for squirrels and other mammals, and enterprising predatory wasps may gnaw their way into galls in trees and on the ground. If the gall wasp larva escapes all these predators and survives to adulthood, it chews its way out, leaving a small neat hole in the papery gall, which falls with the leaves of autumn.

Sliced open to see the larva inside.


( 21 comments — Leave a comment )
Sep. 21st, 2006 01:55 am (UTC)
that is so cool. i had no idea insects could do stuff like that.
Sep. 21st, 2006 02:21 am (UTC)
so there's just one little guy in those pods?
Sep. 21st, 2006 02:25 am (UTC)
They look almost tasty when sliced open like that... :E
Sep. 21st, 2006 11:41 am (UTC)
Agreed. Looks almost like a Kiwi!
Sep. 21st, 2006 06:44 pm (UTC)
yep. and the larva is remarkably handsome. for a larva.
Sep. 21st, 2006 03:11 am (UTC)
My mom used to tell me that if you took a rusty nail and swirled it around in the old, dry-er ones, you could make a cheap type of ink.

This was before I understood quill pens.
Sep. 21st, 2006 03:20 am (UTC)
That is amazing. I had no idea.
Sep. 21st, 2006 04:01 am (UTC)
Thanks bro, I never quite understood those things. I'd heard they were some kind of seed pod and I'd heard they were somehow related to insects. In a weird way I guess both of those are right. Nature is really weird.
Sep. 21st, 2006 04:09 am (UTC)
Galls have large amounts of untapped poetic metaphoric potential. They symbolize:

-The incredibly interconnected genius of nature (duh)
-Nurture, caring

all at the same time...

I sense a poem brewing...

only problem with these sciencey poems I make is no poetry fans understand science well enough. Darn.

But think about it! It's beautiful and ugly at the same time- esp. that cross section, it's striking as all hell, almost astronomical-looking, a shining sun with rays of structure spreading out to the edge of the sphere it's contained in...a shining sun with a MAGGOT at the epicenter...(but maggots are cute babies XD )

Wow. I am having a serious 'wowed by the world' moment here.
Sep. 21st, 2006 04:53 am (UTC)
That is the perfect structure for the classic high school physics class egg drop project.
Jun. 4th, 2009 06:11 pm (UTC)
Mother Nature for making it, Urbpan for helping me figure out what it was, and momomom for relating it to PHYSICS!!!!! Absolutly awesome!
Sep. 21st, 2006 10:37 am (UTC)
It's hard and fun (for me anyway) to try imagine the evolutionary path that finally settled in to this relationship
Sep. 21st, 2006 10:41 am (UTC)
I always wondered what the heck those things are!

The words "gall wasps" always reminds me of Kinsey - his first subject before humans.
Sep. 21st, 2006 11:42 am (UTC)
Well that was quite interesting! I learned something new today!
Sep. 21st, 2006 06:27 pm (UTC)
That is totally freaky fascinating.
Oct. 4th, 2006 05:34 pm (UTC)
They dont even tell u who eats them and wat it eats!
i got homework on this i need to know!
HELP ME!!!!!!!!!!!!!!!!!!!!!!
Oct. 4th, 2006 07:28 pm (UTC)
Re: heyyy
I think I listed some predators (who eats them) in the text above. As to what the gall wasp larvae eats, it is trapped inside the gall, so it must eat material therein. I appreciate you consulting my blog for research, but it is just a blog. There are many good primary sources out there; google "Amphibolips confluenta" and you should have your choice. Good luck!

Sep. 8th, 2008 11:08 pm (UTC)
answered my question
Thanks for this neat information. We had found a few on the ground under an oak tree and wondered what they were. You answered our question!!
Sep. 8th, 2008 11:27 pm (UTC)
Re: answered my question
Glad I could help!
Feb. 20th, 2010 04:50 pm (UTC)
this is cool
May. 18th, 2010 03:37 am (UTC)
The ink thing is real. From Wikipedia: Iron gall ink (also known as iron gall nut ink or oak gall ink) is a purple-black ink made from iron salts and tannin from vegetable sources. It was the standard writing and drawing ink in Europe, from about the 12th century to the 19th century, and remained in use well into the 20th century...
( 21 comments — Leave a comment )


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