Cecidomyia symmetrica, n. sp.
Hard red gall on the leaves of different kinds of oak, small and round (between 0.05 and 0.1 in diameter) when single, but more commonly assuming an irregular shape by the coalescence of a number of them.
I find them chiefly and in large numbers on leaves of Quercus falcata in autumn. They sometimes invade almost the whole surface of the leaf, and have exactly the same size and shape on both its sides. The single round galls contain one larva, the compound ones a number of them, depending on the size of the gall, but each in its own compartment. The red substance of the crust shows many cracks, when the gall is ripe, and is easily detached. Under it is a harder, almost woody, yellowish substance. When the dry leaves with such galls fall to the ground, the red part of the crust generally crumbles away in part, partly it is found erect, forming a jagged fence round the gall. Such galls are generally empty, the larvae having perhaps gone under ground, although one of the specimens which I brought home was inclosed in a delicate cocoon inside of the gall.
These galls, as I remarked before, protrude symmetrically on both sides of the leaf. On other kinds of oak, especially the quercitron oak (Q tinctoria [velutina]), I found similar galls, but on the upper side of the leaf only, without the corresponding excrescence on the under side. Those I brought home were abandoned by their larvae, which went under ground. Thus I am very uncertain about the identity of both galls, as well as about the habits of the insects. As all these galls were found with larvae late in autumn, it is evident the fly escapes very early in the spring.
