Oak galls are created by a group of insects on different parts of a tree. They are formed through a chemical reaction between the hormones of the tree and the fluid coming from the insect. Once the gall is formed, it makes it easier for the insects to build a nest, where they can lay their eggs and reproduce. You can find an oak gall in the roots, leaves and bark of a tree.
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Check the texture of the gall to determine its type. Smooth types of galls are referred to as gouty oak galls. Galls with horns are referred to as horned oak galls.
Look at the ground under the tree and see if there are any galls that have fallen from the branches or leaves. If the wasp inside the oak gall begins jumping off the nest, these are identified as jumping oak galls.
Check the tree for any woody or solid growths in its branches. Stem and twig oak galls are usually produced by wasps and measure about 2 inches in diameter. You will notice them drooping from the branches of the oak tree.
Locate the midribs of the oak tree and see if there are any galls growing with a diameter of 1 to 2 inches. These appear spongy in texture due to the larva of the wasp normally produced in it. This type of oak gall is referred to as an oak apple gall. The galls may cause the walls to become thinner as soon as the mature wasp escapes. These are rather larger in nature, but they are harmless to your trees.