About three years ago, while walking the dog along the Hudson River up here in Newcomb, I came across a beautiful pale green cone-shaped growth at the end of a willow twig. I didn’t know what to make of it at the time, since I knew that willows do not produce cones. Cones are found primarily on conifers (“cone-bearing trees”), but I know of at least one hardwood that has cone-like structures: alders. This was no alder; what could it be? A little research turned up the answer: a pine-cone willow gall.
Like galls found the world over, the pine-cone willow gall is the by-product of an insect-plant interaction. The insect in question is Rhabdophaga strobiloides, the pine-cone willow gall midge, and the plant, obviously, is a willow. Although these midges are found everywhere a willow grows, it is not likely you will ever actually see one, for they are rather small. Or perhaps you might see one and mistake it for a small mosquito, for it is often described as closely resembling one.
As with other galls, the growth’s formation begins when the adult female selects a suitable place in which to lay an egg. In this case, the mother-to-be chooses a terminal leaf bud on a willow. She deposits her egg in the early spring and then nature takes over. When the larva hatches, it exudes a chemical that disrupts the normal growth of leaves and branches, resulting in the creation of a cozy home that to you and me looks like a pinecone. The larva, a little pink grubby thing, takes up residence in a chamber in the center of the gall, where it eats its fill and then waits for winter to pass.
Spring rolls around and the larva pupates. Before long the pupal skin splits open and out crawls the adult gnat (or midge, depending on who you read). Soon it will be off to find a mate and continue the cycle, ad infinitum.
Now, if you are looking for an interesting project to entertain some kids, or even yourself, collect a pinecone willow gall or six around about March. Bring them inside. Using a sharp knife, slice the gall in half, lengthwise, just off-center. If you do it right, you will expose the little pink larva in its cozy chamber. If you do it wrong, you will slice the larva in two (or, more likely, mash the larva). Assuming you’ve left the larva unharmed, place the gall (with its larva) in a jar with a bunch of wet cotton – this will keep the larva from drying out and dying. Put a lid on the jar. Now you can watch as the larva changes to a pupa, and a week or so later into an adult. Pretty cool
Meanwhile, stick your remaining galls into another jar with a wad of damp cotton. You might want to pin them to a piece of cardboard or Styrofoam to keep them upright and off the soggy fibers. Wait and see what emerges. You may get our friend the gnat, or you may get a variety of other insects, from parasitic wasps, to other species of gnats, or even juvenile grasshoppers! I suggest you keep a lid on this jar, too.
Fall and winter are prime times to look for galls, for now the braches and twigs of trees and other plants are exposed to the elements. Some galls are round like gobstoppers, others football shaped. Some have shapes that defy classification. You can find them on goldenrod, willows, cottonwoods, oaks, spruces, and blueberries, to name a few of our native plants that are likely to sport these growths. Take along a sharp pocket knife and slice a few open to see what is living inside. If you find a gall with a hole on the outside, it’s possible a bird beat you to the hidden morsel inside! Gather a few and bring them home; a collection of galls is a wonderful addition to any naturalist’s stash of nature’s endless treasures.