Unusual Insect Gall

The alert observer of the out-of-doors soon learns to expect the unexpected, but it. At first glance, it is difficult to believe that “pine cones” are growing on pussy willow twigs.

Only careful observation will determine that the “cones” occasionally seen on the tips of willow twigs are not cones but are terminal buds that have enlarged and grown in the shape of small cones.

unusual insect gallPin

These are called the pine cone willow galls, which are likely to be found on any of the common species of willow but are seen most often on the pussy willow, Scdix discolor.

The galls are caused by a tiny two-winged fly known scientifically as Ilhabdophaya (Cecidomyia) grobiloides.

These tiny flies, described and named back in 1874, appear in late April and early May.

When the terminal buds start to grow, an egg is laid in the bud, and the tiny larva begins to feed. This feeding irritates the bud cells, and the bud scales elongate into a tight.

Cone-like growth. As in some kinds of galls, this insect may secrete an irritating substance which causes the abnormal development of the bud.

After being infested, the galls are surrounded by an abundance of leaves which partially hide the growth of the gall until Autumn, when the leaves fall.

The tiny larva stays in its cell in the center of the gall throughout the Winter and emerges as the adult fly in the Spring.

The abundance of pine cone willow galls varies each season, but more than the usual number were observed in 1931. Those shown in the photograph were collected on the farm of Donald L. Priest, Groton, Massachusetts.

They offer a pleasant variation from the usual Christmas decorations used with hollies, bayberries, or rose hips.

44659 by Prof. W. D. Whitcomb