Leaf-Rollers
By this name are denoted the larvae of insects belonging to several different orders, and all of which may cause considerable injury to the trees and shrubs in gardens. To herbaceous plants they are less hurtful. The larvae dwell in tubes, formed of the inrolled leaves, and are thus well protected against assaults from without. Many of them have the habit, when the plant on which they live is smartly shaken, of crawling from the leaf-tube, and lowering themselves, by a thread of silk, till the dreaded danger is past, when they pull themselves up by the thread, and reenter the tubes. Advantage may be taken of this habit to shake them on to a sheet laid below; and from this they can be collected for destruction. The leaf is retained in an inrolled form by means of numerous short cables of silk, passing from surface to surface of the roll. Sometimes, the silk is fixed before the leaf has opened originally; but, in other cases, the larvae have been seen at work fixing the threads and drawing the leaf into position. In the smaller proportion of cases, the inrolling of the leaf is due to swelling on one surface, brought about by the irritation caused by the action of the indweller or indwellers. The damage done may be confined to suction of the tissues in the interior of the tube, or these parts may be eaten away, and the leaf may thus be killed. The leading forms of Leaf-rollers are: (1) Moths, for the most part belonging to the group of Tortrices. The insects seldom reach 1in. in spread of wings; but they are at times so numerous as to more than make up for their small size individually. Their wings are generally rather broad, and are usually dark or some shade of brown. Some species almost strip trees of their foliage, e.g., Tortrix viridana on Oaks. (2) The leaves of several of the cultivated Willows have the margins rolled in to form tubes, the agents being larvae of Sawflies of the genus Nematus, or else Gall-midges, belonging to the Cecidomyidoe. (3) Certain Mites also, of the genus Phytoptus, roll the margins of the leaves of some kinds of plants, so as to form narrow tubes, in which they live for protection. Few cultivated plants have the leaves rolled by these Mites; though Hawthorn and Sloe occasionally have their leaves a good deal injured in this way.