Story and photographs By Joan Herrmann

Whereiwander… once again it is outdoors to the meadow and woods and then down to explore our neighbor’s pond. The interesting irritations which I will be looking for are those made by insects laying their eggs on plants. Most animals that lay eggs need to provide a nest. Then they must incubate the eggs and protect the eggs too. Once the eggs have hatched they then will assist in guiding the newly hatched to a source of food. Many insects avoid all that caretaking by inserting their eggs into plants that will unintentionally provide the necessary protection and food.

Once the insect lays its egg or eggs its work is done. The plant senses an irritation and begins to create a growth around the annoyance (the egg). Each plant creates a “unique house” for its uninvited guest which is referred to as a Gall. Of the more than two thousand insects which use this as a means of reproducing offspring about a thousand are wasps or gnats. Oak trees, Maple trees, and Willow trees are reluctant hosts and so are grape vines and numerous plants such as Milkweed and those of the Rose and Daisy Families. Some insects lay their egg or eggs on the buds, leaves, stems, or roots.

The most noticeable gall that I have encountered is the one that can be seen on the stem of a Goldenrod plant. This gall looks like a large green ball within the stem of the plant. The insect which laid her egg inserted her ovipositor into the stem and will lay only one egg per plant. The insect is known as the Goldenrod Gall Fly (Eurosta solidaginis).

Once the egg hatches the larva will secret its saliva within the stem which is an irritant to the plant. The plant reacts much the same way we do when a black fly bites, draws blood, and secrets its saliva onto our skin, and we react by a swelling of the bitten area. The goldenrod plant reacts in a similar manner producing plant tissue around the intruder (the larva) and producing the green gall within its stem. The larva within the gall now has food and shelter throughout the summer, fall and winter. The plant will change color as it ages in the fall and the gall will appear as a brown ball shape on the stem.

Once the temperatures drop the enclosed larva will produce a type of “antifreeze” known as glycerol which will keep it from freezing inside the gall. The larva will remain dormant throughout most of the winter in an insect deep sleep known as diapause. When the temperatures rise and daylight becomes longer in the springtime, the now active larva will chew an exit tunnel through the gall. When it has achieved an exit opening it will lightly seal the exit hole. The larva will now begin the third stage of metamorphosis and begin its pupal stage.

Upon completion of the pupal stage, the adult fly will emerge and will then use the previously chewed tunnel to escape from the gall. The adult fly will pump fluids into its head and pushes its “bubble head” through the lightly sealed exit hole. An interesting note is that the seed production of the goldenrod plant decreases by forty percent as a result of the gall; which is another example of disease and insects keeping our native plants in balance.

The Willow Cone Gall Is another gall that I find intriguing especially since it is the shape of a pine cone. We know cones grow on coniferous trees and we also know that a willow is a deciduous tree, there lies the mystery. The pine cone shape gall on the willow tree is created in a similar manner as that of the gall fly larva except it is created by a tiny midge (Rabdophaga strobiloides). It initiates a gall which may be found at the tip of a willow stem. The gall is produced by numerous stunted overlapping willow leaves.

The cone shape is green in summer but will turn a dark brown in fall and appear a whitish-gray in winter.

The Oak Apple Gall is produced by another wasp (Amphibolips confluent). However, it is only one of more than eight hundred different galls that are produced by oak trees. The oak apple gall is about the size of a golf ball and it is green in summer which gives it an apple-like appearance, but it will appear a papery brown color in fall and winter. Another rather interesting gall is the one produced on Red Maple leaves. It is known as Maple Eye Spot Gall and is rather colorful. The infected leaf appears to have one to several bull’s eyes on it and the gall is produced by a midge (Cecidomyia ocellaris).

A different type of gall is produced on the wild grapevine leaves. Grape Phylloxera gall is a notorious pest of vineyards native to North America. The grape phylloxera gall was accidentally exported to Europe in the mid-1800s, nearly destroying the French wine industry before resistant rootstocks were shipped from the United States to salvage the crops.

In addition to the numerous species of insects utilizing this method of protecting their eggs throughout the seasons, and their metamorphosis stages, galls may also be produced by fungi, nematodes, and bacteria. Galls may actually be beneficial in a win-win situation in that the insect derives food and shelter and the plant doesn’t suffer too severely. Humans have also found ways in which to profit from the galls too in that some medicines, insecticides, and even permanent inks benefit from the substantial amount of tannic acid they contain.

I hope that you will have a pleasant and interesting summer and perhaps will have an opportunity to discover some of these “interesting irritations”. It is especially fun to share some of these facts with children and grandchildren.


As a Professional Nature Photographer, Naturalist, and Outdoor Educator, Joan Herrmann has been teaching and doing programs for Schools, Garden Clubs, Libraries, and Nature Centers, for about 38 years. After moving from the Rochester area in 1995 she began her Photography business, Essence of Nature, and also became a co-owner of The Artworks in Old Forge, New York. As a docent at Munson, Williams, Proctor Arts Institute, in Utica, New York she has been educating children and adults, for nineteen years.

In 2007 she began working with the Black River Outdoor Educational Program (BROEP) and in 2013 and 2014 did a week-long summer program at BROEP in conjunction with Mohawk Valley Community College (MVCC). Using her love of both nature and photography she created a Flora/Fauna outdoor educational program teaching students (ages 6 to 14) the joys of nature and creative photography skills.

Joan’s love of nature has been a lifelong study of Birds, Wildflowers, Mosses, Ferns, Trees, Amphibians, Reptiles, Grasses, Insects, Spiders, Tracks, Scat, and Galls. She has assisted in the cataloging of all trails used by the hiking Coaches and photographed and identified seasonal Flora.

Since October 2016 she has been writing a bi-monthly nature column with Adirondack Express Newspaper. In October of 2019, she began a bi-monthly column with the My Little Falls Newspaper. You may reach her at jmhphoto8442@gmail.com