From: jim.speirs@canrem.com (Jim Speirs) To: dannys@iis.ee.ethz.ch (Danny Schwendener) Subject: Those Curious Galls Summary: Ben Kruser explains what insect galls are (those weird bulbs found on plants) and how you can bring this theme into your activities. Article #R123. ============== Those Curious Galls Ben Kruser The Leader, November 1990 Nature abounds with curious things, and insect galls are one of the most overlooked of them all. Now that fall is ending and most leaves have dropped, you can add gall hunting to your list of simple outdoor activities for everything from Beaver rambles to outdoor training for adults. Galls are abnormal woody growths found on many species of plants. They are caused primarily by a wide number of insects, mostly midges and sawflies, which have adapted to depositing their eggs in the green, growing tissue of certain plants. One type of common gall, for example, is the pine cone willow gall, a grey-green pine-cone shaped growth found at the end of willow stems. When a gall midge is ready to lay her eggs, she seeks out a suitable green willow bud. Generally, these buds are made of soft plant tissue in the stage of growing and dividing. In the summer, the female midge uses a special stinger, called an ovipositer, to puncture the bud and deposit the egg inside the plant. Midge secretions left behind with the egg stimulate the bud scales into rapid growth, and the egg becomes encased with ever-growing layers of scales. When the egg hatches, the larva eats out a chamber and continues to secrete fluid that stimulates scale growth. By the time fall sets in, the larva has become a dormant pupa, and the bud a thick, pine cone shaped fortress. As are other galls, the pine cone willow gall is a prime example of specialized insect adaptation to the harsh winter environment. A good majority of bugs survive in the form of future offspring after the adult lays eggs in the fall before cold weather kills it. Some larvae overwinter in cocoons hidden under loose bark for protection. Cocoons, however, do not offer much protection from bark prying predators such as chickadees and titmice. Bugs that use rotten trees and logs for hiding larvae give them more protection, but even they are vulnerable to woodpeckers and skunks. Galls go a step further by incorporating a woody barrier with camouflage. Some common plants and places to look for galls are: - Goldenrod: Stem (Goldenrod Ball Gall); Flower tip (Goldenrod Bunch Gall) - Oak: Leaves (Oak Apple and Potato Gall); Stem (Wool Sower, Hedgehog and Bullet Galls) - Wild Rose: Stem (Spiny Rose Gall) - Poplar: Stem (Poplar Stem Gall) - Willow: Bud (Pine Cone Willow Gall) Also look on grape, sumac, elm, hackberry, and nettle. So far, we've talked about insect-derived galls. Some galls are caused by fungus and viruses. Common ones to look for are Cherry Smut, burls, and Cedar Apples. You'll see Cherry Smut as a black cankerous growth on cherry twigs. Burls are large tumours on tree trunks, often used to produce burl veneer products. Cedar Apples on red cedar are the rust stage of a specialized fungus. The disease also requires hawthorn or cultivated apples and their relatives as another host. On wet spring days, the cedar apples develop yellow horn-like spouts that bear spores carried by wind to hawthorn or apple. Yellow-orange spots--the growing fungus--appear on the apple tree leaves. The fungus then infects red cedar again via wind-borne spores, and the cycle continues. People have used galls for hundreds of years. Ancient writings mention the Aleppo Gall found on species of Asian oaks. This gall contained about 65 percent tannic acid, which made it valuable in producing astringents for treating burns, mouth infections and toothaches. The high tannic acid contents of other oak galls were used to make ink and dyes. In fact, many early government documents were written with gall rendered ink. Unfortunately for insects, their charade of hiding eggs and larvae in plant tissue has not gone unnoticed. Woodpeckers, mice, and squirrels are known to eat the gall's nutritious grubs. Activity Ideas The next time you're in an old field, look at dry wildflower stems, especially goldenrod, for galls. Examine the gall for its structure and, if it's early spring, see if there is a little exit hole where the newly emerged adult crawled out. With a sharp knife, you can cut the gall in half to examine the fibres inside, and perhaps even find the larva. If you find a gall with no exit hole this winter, you may wish to put it in a jar and wait until spring to see what emerges. lt will give you an opportunity to discuss with your group various types of life cycles and the interrelationships of plants and animals. Program Links Beavers: Special animal homes; plants and insects sharing; winter food Cubs: Black Star 2,1 l; Observer 5 Scouts: Conservation Bronze 3d, Naturalist, Science, Collector Venturers/Rovers: Talk with a botanist or entomologist about life cycle habits and the biology of galls.