I notice on page 7 in the January number of the Gardener's Monthly, that some of your correspondents still indulge in chronic complaints about the two noxious insects I have named above, and of course, they complain because they are afflicted. Now this ought not to be, especially so far as the matter relates to the insect first named - the "Bag-worm." In the whole catalogue of noxious insects I do not know of one that is more accessible, more conspicuous or easier managed than the one just named. It does not make the least attempt to escape, and could not if it would. At the least interruption it immediately withdraws itself within its case, and unresistingly submits itself to whatever fate may be impending; and, if it escapes final detection, it must be from a want of human vigilance; and my main object in writing this, is, to admonish all sufferers from the defoliations of the Bag-worm, or whatever other name it may be known by, that now is the proper time to destroy it - now - when all trees except evergreens are leafless, and these enemies in embryo, ensconced in their spindle-shaped follicle, are so conspicuously dangling from their branches. As you intimate in your reply the war against marauders should be general and simultaneous.

It is true that on the Arbor Vitae they are not so visible as they are on trees or shrubbery that shed their leaves; but, if the matter is attended to from now on to the middle of April, or even the first of May, a united and vigilant effort must succeed. The leaves of evergreens which form the outer clothing of their follicles become discolored as spring approaches, and these faded masses are in positive contrast with the living green of the trees, pointing out just where these stealthy enemies are located. Although the larger number of these follicles are the deserted habitaculi of the males of last season, yet not one of them should be allowed to remain. The pupa-shell of the female remains in the case all winter, and this shell is filled from top to bottom with eggs - 300 to 500 in number - nicely packed in short silky fibers that she rubbed from the hind end of her body in the process of oviposition; and no amount of cold can affect them, nor can the least moisture reach them, or any bird dislodge them.

It is easily seen then, that if a single follicle, so charged with eggs, is overlooked, enough of the worms will be evolved to inoculate a very large tree, or a pretty long Arbor Vitae hedge. True, they are subject to adroit insect parasites - several species of them - and no doubt many are destroyed from this cause; still, they are so completely protected, that they are better able to elude the attacks of their parasitic enemies, than the naked caterpillars which have no protection.

On one or two occasions I have observed the exclusion of the young bag-worms from the eggs, and it was to me an interesting sight. On one of these occasions the metamorphosis took place in my sanctum. I had two follicles hanging on a nail in the wall all winter, one of which was that of a female. The room was kept warm, and of course, the evolution was premature, occurring in April. The young emerged from the mouth, or lower and open end of the bag, one or two at a time, each one spinning his own silken cord. They were very lively, "paying" out the cord with great alacrity. Wherever, or upon whatever they happened to alight, there they soon began to construct their habitaculi. Some of them alighted on the wall and these constructed their small cone-shaped houses out of scales of whitewash; some fell upon the leather cover of a book, and these appropriated small scales of leather, whilst others fell to the floor, and for the same purpose appropriated small scales of a rush carpet that covered the floor. These juvenile follicles are not spindle-shaped, but cone-shaped and stand erect; it is only after the inmates become eight or ten days old that they become pendant.

On the 26th of May I hung a single follicle on a quince tree, and on the same day they came tumbling out in rapid succession, to the number of one hundred or more, when I destroyed the remainder by throwing them into the fire; in less than half a day none could be discovered; but on the branches, and under sides of the leaves, their little erect cones projected like so many small spurs, and if I had not known that they were there, I probably would have overlooked them altogether. It, therefore, is important that the follicles should be destroyed before the young reach that period of their development. Let sylviculturists and horticulturists "stick a pin there".

Although these insects seem to have a preference for the Arbor Vitae - at least in some localities - yet I have found them much more destructive to a few other trees, especially the linden and the silver maple. It would be hard to say what tree they do not attack, except perhaps the peach. But in addition to the various species of conifera, I have observed them in great abundance on locust, linden, maple, cherry, plum, apricot and apple; also on the roses, quinces, lilacs, walnuts, chestnuts, oaks and others. I think the largest number I ever saw together in one place, was in a small locust grove in York county, about forty years ago.

My attention was called to them here in Lancaster, in the summer of 1849, by a gentleman who had a fine apricot tree, the leaves of which became as crisp as if they had been scorched, about the end of August, for several seasons, every year becoming worse, and he could not divine the cause. I called his attention to the fact that those shriveled bunches of leaves were on the move from one twig to another in search of fresh pasture. After he knew the cause, it was not long before he gathered and made a general roast of them, after which his trees fully recuperated again.

I know no effectual remedy but hand-picking, and with a pair of garden shears attached to a long pole, and worked with a cord, a pretty large tree can be entirely cleaned.