Insect Galls

By Jennifer Correa-Kruegel

“Ewww! What is that on that leaf?” exclaimed a student pointing to a large grouping of abnormal growths on a leaf. It was during a Conservation Photography class where students are encouraged to look at things around campus with a different perspective than they normally would. So it was no surprise to me that this student picked up on numerous galls that developed on the leaves of trees recently.

Insect Gall

Insect galls are a result of a plant’s response when an insect lays its egg on part of the plant, such as the leaf, roots, or stem. The plant tissues react to a substance on the larva and surround it with a casing, protecting it while the insect matures and eats until it is ready to emerge. Insect galls can be made from insects such as flies, bees, wasps, moths and mites.

Insect Gall

While galls provide some protection from predators, the larva is not completely safeguarded. If there are too many galls or if they are too obvious, animals such as woodpeckers can easily dig out the immature insect. Gall inducing insects are usually particular as to which plants they lay their eggs on since only certain species of plants will respond appropriately to their larva. This is noticeable as you can see the very detailed differences of each gall. A gall on one species of plant will look very different from another.

Insect Gall

Although galls are parasitic to the host plant, it is unusual that the plant itself will die from the galls produced unless it is a very heavy infestation. We see so many galls in the spring because insects take advantage of when the plant is at its most productive stage of growth. However, there are plants that develop later in the year, such as goldenrod, and the insects that use those plants as a host will use that opportunity to create their galls and have the larva undergo its changes throughout the winter and eat its way out the following Spring.

The students were fascinated by the unique and sometimes strange shapes and colors of the galls. They can be found throughout campus if one looks loosely enough at the leaves of emerging plants. Although galls are not the most beautiful sight to witness, it is interesting to see the interdependence and connections made throughout the natural world, no matter how small.