With temperatures dropping and the first waves of fall color visible in the treetops, October is the perfect time to venture back into the dune forests that have been filled with mosquitoes and other flying insects all summer. Most of those insects, active since May, will not be seen again until warm temperatures return in the spring. A curious and watchful hiker, however, can still find signs of some of these insects in the form of galls.
A gall is an abnormal growth on the stem or leaf of a plant caused by an insect, and is used by that insect for food and shelter while it develops from a larva into an adult. More than 1,500 insect species have been documented using galls. A gall is formed when an insect pierces a stem or leaf and lays its eggs on or in the plant. The plant reacts to this wound by growing around the eggs to protect itself. Unwittingly, this provides the egg with a warm and safe place to hatch, as well as a food source for the larva. The larva will eventually eat its way out and fly away as an adult insect.
One of the most commonly seen galls is that of the Goldenrod Gall Fly. Explore any patch of goldenrods this winter and you will almost certainly find at least a few round galls along the main stem of the plant. In some cases, you might find a hole drilled into the side of the gall. This may be a sign that the larva has developed and left the gall, or it may be a sign that the gall has been visited by a predator. Parasitic wasps will lay their eggs in an already formed gall. When hatched, the wasp larva eat the insect larva. Downy Woodpeckers can also be seen perched on a goldenrod stem, pecking into the galls to eat the fly larva. It is amazing to think about the epic life and death struggles going on in one small patch of dried up goldenrods!
To read more about galls and other wonders of the winter woods, check out A Guide to Nature in Winter by Donald Stokes. Thanks to Dunes To You educator, Matt Beatty, for today's natural insights!