Golden Rod Gall Fly (Eurosta solidaginis)

2 March 2020

Plants of any species are not exactly clamouring to be observed in this deep snow and cold, but we happened upon a dried Golden Rod (Solidago sp.) sticking above the snow with a large gall on the stem. There are three species of insects that form these galls but which can be differentiated by the shape of the gall that results. This one is spherical, known as a ball gall and formed by the Goldenrod Gall Fly, Eurosta solidaginis. The adult insect lays its eggs on the plant in the early part of the year. The larva from the hatched egg then eats its way into the stem and the plant responds by rapidly increasing cell growth around the intrusion, enveloping the larva in a woody protective sheathing that keeps the larva safe, and provides a food supply for the remainder of the summer and a home to overwinter in before emergence in spring as a new adult. The larvae are not entirely safe, however large and hard the gall appears to be – Black-capped Chickadees and Downy Woodpeckers have this food source worked out and can break the galls open to eat the larva inside