This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
Of the shade trees, the Lime or Basswood suffers most, but the Elm, Weeping Willow, some varieties of the Maple, the Horse Chestnut, and some other kinds, are also more or less involved. And although the span worm will feed upon the leaves of almost every tree, it seems in most cases to be from necessity and not from choice. The eggs of the span worm are seldom found upon the Ailantus, the Catalpa, Paper Mulberry, the fruit trees, and never on the Black Walnut, nor that fine shade tree, the American Tulip, (the Liriodendron tulipifera).
It is often the case, that in planting trees we set out more than are wanted as they increase in size. When they are all permitted to stand they crowd each other out of shape. Often one tree, with a free chance to spread out, naturally will give you more shade, and certainly be more ornamental, than half a dozen that interfere with each other. The thinning out is often neglected too long, from the very natural reluctance to cut down a tree. I do not know that this is the case in your city; but if you have rows of Limes or Elms, where the trees will crowd each other as they become larger, and if you do determine to subdue the worms, now would be a good time to thin out. By cutting them away and burning them while the eggs are upon them, you will diminish the labor immensely. But I do not wish to be understood as recommending that the trees should be cut down to get clear of the worms. I would not dispute the title to such barbarism with your aldermen.