There
are showy goldenrod plumes everywhere now, and it can’t be too long until the
first hints of purple asters appear. In the unmowed periphery fields of Anna
Maria, the goldenrod clones are particularly tall and healthy looking.
Now is
the time to examine them closely for galls, visible as cancerous looking lumps
in the midst of their slender stems. These were formed by the plant itself, in
a bit of self trickery induced by a parasite that lives within, the gall fly
larva.
When
the plants were mere shoots in late spring, the gal fly female laid eggs on its
exterior. The newly hatched larva secreted a chemical that caused the plant to
develop the gall structure, in which the larva lives within in the soft plant
tissue, while the exterior provides a tough protective layer.
In
August, as the gall nears its full capacity, the larva too have grown within,
spending a portion of the month chewing away a tunnel just to the surface (but
not through) of the gall. Then, it settles down to ready for over-wintering,
using the gall as a sheltered home.
In
early spring, the larva transforms into the adult gall fly, piercing through
the thin remaining layer of the gall shell and beginning the cycle anew when
the first goldenrod shoots arrive.
Look
closely at the galls now; many will have drill holes pierced into them, made by
birds like the downy, who have learned to seek out the larva within.