I came across an old friend in a southwest Ohio county park over the weekend: the wart‑like, irregularly shaped galls, known as "bladdergalls," adorning the upper leaf surfaces of a red maple. The galls are produced under the gene-manipulating direction of the Maple Bladdergall Mite, Vasates quadripedes (family Eriophyidae). The mite also produces bladdergalls on silver maple.
I've taken so many pictures of these galls over the years that I almost walked past without snapping just one more. However, I needed my gall-fix, so I took around 20 gall-shots.
I'm probably not alone in these galls being one of the earliest, if not the first, to open my eyes to the wide world of plant galls. Nevertheless, mine is a cautionary tale. I did not know that maple bladdergalls are a gateway-gall; they can lead to a serious hard-core gall-addiction. Before you know it, you're standing before groups of people saying, "Hello, my name is [your name here], and I'm a gall-oholic."
My gall-habit stemmed from learning the fascinating story behind plant gall formation; read on at your own risk! Eriophyid mites direct gall-growth by inducing plant genes to activate and deactivate at just the right time to cause newly differentiating leaf cells to form the same plant structure; the tiny cigar-shaped mites live inside the bladdergalls. Vasates quadripedes never produces any other type of gall. The equally common maple spindle galls are produced by a different eriophyid mite, V. aceriscrumena; this species never produces bladdergalls.
Other eriophyids produce similar looking bladdergalls on the upper leaf surfaces of a wide range of plants. The Black Tupelo Bladdergall Mite (Eriophyes nyssae) produces galls that look very similar to those found on red and silver maples. The photographs of these galls also show the handiwork of another eriophyid gall-maker. The crinkled leaf edges are caused by the eriophyid, Eriophyes dinus, and are sometimes called Black Tupelo Leaf Roll Galls.
One my favorite plant galls are produced by the Poison Ivy Bladdergall Mite (Aculops rhois (= A. toxicophagus)) on its namesake host. The galls vaguely resemble the itchy skin blisters we suffer when we contact the plant. I like to imagine that gall-infested poison ivy plants suffer the same agonizing itch; but they have no fingers!
I've found that boxelder (Acer negundo) can challenge the saying "leaves of three, leave it be," and the handiwork of the Boxelder Bladdergall Mite (Eriophyes negundi) doesn't help. The galls bear a striking resemblance to those on the three leaflets of poison ivy. However, the boxelder bladdergalls undergo a distinctive change in appearance as they "mature." Early on, they appear as small bladdergalls. Later, they become much larger and produce velvet-like patches on the corresponding lower leaf surface. They are even given a different common name of "Boxelder Velvet Galls." I originally thought bladder and velvet galls were the work of two different gall-makers, but the literature attributes both types of galls to the same eriophyid mite.
Galls produced by the eriophyid, Eriophyes brachytarsus, are another type bladdergall that changes form as they mature. At first, the galls look like typical bladdergalls and are called "walnut bladdergalls" in some online references. However, as they mature, the galls become distinctively pouch-like and are referred to as "walnut pouch galls." Eventually, the galls break open like popcorn to reveal tufts of silvery-white hairs.
Unfortunately, eriophyid mite taxonomy is far from complete; there are many plant galls that are produced by unnamed eriophyid mites (= unknown species). The bladdergalls that occur on several species of willow, particularly on black willow (Salix nigra), are produced by an eriophyid in the genus Aculus. However, the exact species has yet to be described.
The tiny, green, bead-like bladdergalls that arise from the upper leaf surfaces of birch are clearly the handiwork of an eriophyid mite(s). However, the exact species responsible is not yet known.
As with the vast majority of plant galls produced by arthropods (e.g. wasps, midges etc.), those that are induced by eriophyids cause little to no harm to the overall health of their plant hosts. Indeed, I contend that they add ornamental value to their tree and shrub hosts. Of course, my name is Joe Boggs, and I'm a gall-oholic.