Maple Spindle Galls
On July 4, 2024, Sam brought me a maple leaf with these little elongated galls all over them. The individual galls were about the length of this dash – . These are Maple Spindle Galls, which are caused by the microscopic mite Vascates aceriscrumena. These mites hide in the bark of the tree branches for the winter, and then in the spring they crawl onto the developing maple leaves. They then irritate the growing leaf into producing these characteristic growths, which are basically leaf tumors. The mite then lives inside the gall sucking on plant juices. There are apparently only female mites, they reproduce asexually while they are in the galls. Then, in the fall, the mites crawl out of the galls and hide in the bark until the next spring. They don’t do any serious harm to the maple trees, and in fact don’t even cause much deformation of the leaves.
Here are a couple of zoomed-in images of some of the galls from the side, and from the top:
And while looking at these images just now, I saw something very odd right at the limits of the resolution of my macro lens. There are these little red dots that look like they are on tiny stalks, and follow the main vein in the leaf.
I do not know what these dots are. I can’t find anything about them, probably because they are microscopic and so they are unlikely to be noticed under normal circumstances. They aren’t even visible with the macro lens unless I have the magnification wound up all the way. They could be tiny mites sucking plant juices out of the veins, or they could be fruiting bodies of some sort of fungus, or heck, I don’t know, they might actually be a natural part of maple leaves. I suppose it is possible that they are the actual spindle mites, who may have emerged from their galls to suck juices as free-living organisms before they go into hibernation.
I’ll have to look into this further, but I am not too hopeful of finding out anything much further about them.