Large Flies Have The Gall To Damage Goldenrods Goldenrod galls on the stems of Canada goldenrods. The two holes were made by downy woodpeckers in search of the larvae. The conspicuous remains of many plants poking their heads above the late winter snow are a pleasant reminder of their forthcoming descendants and the much-awaited greenery of spring. Diverse forms of dozens of plants are readily identifiable, some even when viewed from a moving automobile. When driving through swampy areas we invariably admire the fragile-looking fluffy cotton-like masses of fruits of the Virgin’s Bower plants, commonly called climbing wild clematis, Clematis virginiana. They cling to shrubs and small trees growing in damp areas. One of our favorite plants that grows in the rich soil of wet shrubby ditches or along steams in east-central Wisconsin is the prickly or wild cucumber. This decorative but inedible high-climbing annual, relative to squashes, is sometimes referred to as the wild balsam-apple. Its prickly oval pods are very unique. Thousands of Queen Anne’s lace and cow-parsnip plants hold their many-rayed, somewhat flat-topped umbels well above the foot of snow. Soon the fallow fields and roadsides in all directions will be decorated with their intricate forms and beauty. While cross-country skiing or snowshoeing through the edges of woods bordering some of the frozen-over swamplands we encounter the stiff, dark brown, fertile fronds of ostrich and sensitive ferns protruding above the snow. Their presence on these cold days is a gentle reminder that, come June, the snow will be replaced by hoards of mosquitoes in these secluded and pristine glens. Silvery-lined milkweed pods, their flat seeds already parachuted to distant places, bring to mind the monarch butterflies that arrived during early June last year in search of the young milkweed plants so vital in their life cycle. Hatched monarch caterpillars ravenously ate the leaves of only the milkweed plants of several species. An excellent book, "Pods: Wildflowers and Weeds In Their Final Form," will help you to identify the remains of last year’s herbaceous plants. It was written by Jane Embertson of Wauwatosa. Outstanding photographs show exquisite forms of the plants as found in nature as well as these same plant remains used in dried arrangements. Using plant remains at this season generally produces little risk if any to the survival of the species. Frequently seed dispersal has been completed by now. Just to be on the safe side, check the current regulations protecting certain plants, and avoid collecting in parks and sanctuaries. One of the most distinctive and tenacious plant forms gracing the outdoor scene throughout the year are the ball-shaped galls existing on so many goldenrod stems, especially those of the Canada goldenrod. These spherical formations were instigated by tiny attractive black-mottled-winged flies belonging to the genus Eurosta. I call them goldenrod flies. Being about the size of house flies, but related to fruit flies, these creatures mate during the summer. Plant tissue of a goldenrod stem is pierced by the female’s ovipositor and an egg is deposited in the wound. Healing soon covers the small opening thereby sealing the egg inside the expanding tissue. The injury to the stem alters the plant’s chemistry at that point resulting in a globular enlargement that is referred to as a goldenrod ball gall. The egg hatches and the larva lives within this tiny chamber lined with a layer of juicy thin-walled cells, the pith of the gall. As the cells are eaten they are quickly replaced for as long as the tiny quarter-inch-long cream-colored larva inside requires food. The outer hardened cells of the gall serve as protection for the creature. A truly amazing thing happens before the larva changes into its pupal or cocoon form. It consumes the plant tissue toward the outer wall and, in doing so, produces an escape tunnel right up to the paper-thin outer shell. This tunnel does not close in. Having done that, the larva squirms back to the central chamber where it undergoes the next stage in its metamorphosis, the cocoon. Without the escape tunnel the goldenrod fly, having emerged during early summer, would have no way of gaining its freedom. Lacking chewing mouth parts, it would be imprisoned. Properly prepared, it now crawls through the escape hatch, perhaps dissolves the thin outer plant tissue with body fluids, and flies away. Tiny, very neat round holes in the old galls next summer, from last year’s plants, will indicate that the occupants have left. What a miraculous life cycle! Some of the fascinating mahogany-colored ball galls you find now will have been visited by downy woodpeckers. A small excavation, always on the side of the gall, reveals the dark, opened, and empty interior. The larva will have been "fished" out by the woodpecker’s long barbed tongue. Charlotte asked me is I knew that one of the goldenrod galls in the dried bouquet on the table was named Charles – Charles de gall! The only answer I could groan in reply was, "Yes, and have you heard that the little Eurosta flies that inflict so much damage to the goldenrod plants have a lot of gall?" This column appeared in the Door County Advocate on 02/18/2000. © Copyright 2000 Roy Lukes. All rights reserved.