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Oak Apple Galls

May 20, 2010

Over the weekend, Christopher brought me these little balls out of the woods.  They were growing on a very small tree that looked like an oak.  After doing some research (I love the internet) we found out they are called Oak Apple Galls.

These galls are very young. They form when a female wasp (Amphibolips confluenta) injects her egg into the developing leaf of an oak tree.  The tree then forms a gall around the insect…protecting it and providing it with what it needs to continue developing.

I have seen these my whole life, but only in their later stage, and I never knew what they were.  The ones I have seen are dry, brown and had a paper-like feel to them.  There is usually a small hole where the adult wasp bored its way out.

These young galls are green, pliable and still have the developing larva of the wasp inside.  The inside of the gall has this wispy membrane structure, and in the center is a hard core that has the wasp larva.  (We cut all four open and none of them had reached the pupae stage yet.)

I found a cool picture where the white wasp pupae can be seen, on another blog, here.

From what we have read, the life cycle of this insect is very interesting.  Adult wasps hatch from galls in June and July.  Males and females mate and then drop to the ground.  Female wasps then burrow into the soil at the base of the tree and inject eggs into the roots.

Wasp larvae hatch and munch on the roots for over a year before becoming pupae.  Only wingless female wasps hatch from the pupae underground. These females crawl out of the soil and up the tree trunk in early Spring.  They find a newly growing leaf and inject an egg into the mid-rib (center vein).

The larvae that hatch inside the leaf are small and round.  As they grow, they cause a chemical reaction inside the leaf that forms a gall around the larvae. The gall itself is actually a mutated leaf.  Each larva continues eating and growing, and the apple gall grows with it.  Apple galls get their name because large galls look a little bit like apples.

University of Minnesota

One article I read, said that the adult wasp is very tiny…not much bigger than a gnat  (that’s comforting after seeing that picture of one).

Each apple gall only has one larva inside. When the larva is full-grown, it pupates (resting stage) and comes out as an adult wasp. These adult wasps have wings, are small and dark, and can be either male or female. After drilling its way out of the gall by making a hole, each wasp finds a mate and starts the cycle again.

Oak Apple Gall Wasps only lay their eggs in the leaves of oak trees, especially Black Oak, Scarlet Oak, and Red Oaks.

Apple galls can be homes to parasites, inquilines, and other organisms. An inquiline is an animal, or other organism, which uses the gall for shelter, but does not hurt the wasp larva inside. Parasites may injure or kill the wasp larva.

In Winter, when leaves have fallen, trees can look very strange if they have many apple galls hanging from them. These wasps do not hurt the tree, but heavy infestation (many wasps) can cause leaves to fall early.

So there you have it, homeschooling science at its best!

2 Comments leave one →
  1. May 22, 2010 7:21 pm

    That’s really cool Michele! We never have anything cool like that lying around. LOL!

  2. Michele permalink*
    May 22, 2010 7:40 pm

    You’ll have woods with the new house, Tawna. You might!!

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