Trail End There are several things to notice as you walk down the road to finish your hike. The field on the left contains goldenrod (Solidago spp.), a common species whose golden flowers mark the end of the summer. In the winter look for the remnants of goldenrod and the other field wildflowers above the snow. Notice the ball-shaped swelling in the stems of some goldenrods. These are called galls. Galls are formed when a particular species of fly lays its eggs in the goldenrod. As the fly larva develops, the stem tissues grow around it and form the swelling. You may note that some of the galls have holes pecked into them by downy woodpeckers, which feed on the larvae. Take an unopened gall home with you. Place some soil in a large mouthed jar and insert the stem into the soil. Keep the soil moist, keep the jar away from direct sunlight, and cover with cloth. In a few months, the adult fly should emerge. Another species of fly forms galls in willow trees (Salix spp.). Look for the swellings which resemble pine cones on the ends of the twigs of willows growing along the ditch. The larvae overwinter within these swellings and emerge in late spring as adult flies.