The improbable looking but appropriately named Willow Pinecone Galls are now large enough to be very noticeable on their namesake host. As the common name suggests, the galls closely resemble pine cones with closed seed scales. They are produced on willow by the gall-midge Rhabdophaga strobiloides (family Cecidomyiidae), but cause no appreciable harm to the overall health of their willow host. In fact, I believe they add ornamental value!
Online references indicate the galls may appear on a number of willows; however, I've only ever found them on black willows (Salix nigra). This means that a great place to look for the galls are in riparian areas as well as wetlands. If you find the galls on other willows, please drop me an e-mail to let me know the species and location.
The galls have been reported to occur from New England to California. Indeed, during our BYGL Zoom Inservice yesterday, Jim Chatfield (reporting from Utah) showed a picture of the galls that he found on a willow in Grand Staircase Escalante National Monument in southern Utah.
Slicing the galls open lengthwise at this time of the year will reveal a single, tiny, orange colored midge fly maggot (larva) nestled within an elongated chamber at the center of the gall structure. The chamber is protected by multiple layers of cone-like scales.
Female gall-midges initiate the formation of the galls when they lay a single egg in terminal buds in the spring. Chemicals injected by the female coupled with chemicals exuded by the egg and then by the resulting maggot direct the stem tissue to stop elongating and the nascent leaf tissue to broaden and harden into the shape of scales on a pine cone. The maggots develop inside the galls throughout the growing season and remain in the galls through the winter; they pupate in the spring.
I consider plant galls to be one of Nature's true wonders and this gall is certainly a wonder! Who would ever expect "pine cones" to appear on a willow? In fact, they are such dead-ringers for conifer cones, I'd recommend cutting a few galls from a willow and removing anything that gives away the host; then ask others to guess what they are … they make great conversation pieces! Of course, some anti-gallite may tell you to "get a life," but that's another story!