February 11: temperature in Southwest Ohio at 3:30 pm. is 65F. This has been a weird winter. Venturing out has seldom required layering-up to resemble the Michelin Man®! I was rewarded on my "winter" walk today by finding a new treasure trove of willow pinecone galls; hundreds of galls on several black willows (Salix nigra) in a county park. The white galls were easy to spot on the denuded willows sprouting from the tips of twigs.
Arguably, one of the weirdest galls found in Ohio is produced on willow by the gall-midge, Rhabdophaga strobiloides (family Cecidomyiidae). The gall's appearance isn't weird; it looks like a pine cone. However, finding a "pine cone" on a willow is weird. As the common name implies, the Willow Pinecone Gall, which is sometimes called the "pine cone willow gall," closely resembles a pine cone with closed seed scales.
Slicing the galls open lengthwise at this time of the year will reveal a single, plump, 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.
The maggots will pupate in the spring. The resulting female midge flies initiate the formation of new 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. Early-season galls are ball-like; late-season galls are cone-shaped.
Reports in the literature indicate these galls may be found on many species of willow; however, I've only found them on black willow. In fact, most of my images were taken on two black willows growing along a stream near my home. I've not considered these galls to be common in southwest Ohio which is why I was thrilled with today's discovery!
I consider plant galls to be one of Nature's true wonders and I like to share my enthusiasm. While taking pictures of today's gall-bounty, a hiker stopped to ask which bird I was photographing. I showed her the true focus of my camera and she asked if they would kill the trees; a common reaction to plant galls. I explained the intricate dance between the midge fly and its willow host and noted the galls cause no appreciable harm. Her response was rewarding: she never knew such a thing existed and promised to be on the lookout for these and other galls so she could share the gall-story with her children. Another gall-conversion; it was a good day.