This insect commits sad ravages upon our cultivated trees of various kinds, for it is not a choice feeder, consuming but one species, like many other insects. Their most common pasture is the mulberry, and the related Osage Orange is frequently attacked. The Elder bushes appear very attractive to them, and are often covered with their unsightly webs. Elms suffer very much; our favorite fruit trees are attacked; apples, pears, cherries, quinces, and, occasionally, even the peach trees are eaten by them. Even the repulsive Ailantus, which has often been recommended as a wormless tree, is greedily devoured by these caterpillars, notwithstanding its disagreeable odor.
The eggs, from two to three hundred in number, are deposited on the under side of a leaf, near the end of a twig. These soon hatch, and the larvæ commence feeding on the upper surface, spinning their threads from side to side, and then, attaching two or three leaves together, they soon make a web. They continue feeding and spinning along the twig, as they consume the tender portion of the leaf, leaving the mere skeleton.
The caterpillars are small, of a pale yellow color, with a broad blackish stripe on the back, and another beneath. They are thickly clothed with whitish hair; the head and feet are black. Worms of the same nest vary in size and colors. When about an inch long, they disperse, and spin their cocoons. The moth is milk white, without any markings on its wings, and is 1.25 to 1.35 inch in width. (Vide Harris, p. 358).
Though called the Fall Web-worm, these caterpillars appear about Cincinnati in the end of May quite abundantly, and from that time until October, they are more or less frequent; most so in August. In the North, they may be later; I have seen large tracts of forest defoliated on the lake shore, in August, 1865.
Remedies.—For the destruction of these pests we must resort to hand-picking, when they are in the caterpillar state. The twig or branch should be taken off, and the worms crushed or burned. It is fortunate for us that they are gregarious and that they spin a web, for we can detect them while they are yet young, and when confined to one or two leaves, so that the whole brood may be destroyed with very little effort. Birds, and some insects, aid us in keeping them in check.
Clisiocampa decipiens, (Walker), or C. Americana, (Harris), is commonly known as the Tent-caterpillar, or Nest-caterpillar. The larvæ are not indiscriminate feeders, but prefer the foliage of certain members of the Rosaceous family of plants. Their natural food appears to be the common wild cherry, but they attack the apple so vigorously, that they are often called the apple tree worm. Mr. Fitch thinks they do not feed upon the peach; but I have frequently found them upon this tree since 1855. The moth appears to be endowed with wonderful instinct in depositing her eggs; selecting a terminal shoot that has completed its growth, they are placed to the number of 200 or 300 around it in a broad ring or sheath, and covered with a sort of varnish that protects them.
Very early in the spring, when the buds of the apple have just begun to swell, the eggs hatch, and the little worms traverse the twig, spinning a slender thread; when they reach another branch, they halt in the bifurcation, and, moving about, soon create a slight web with the silken threads, and from this they emerge in search of food, spinning a thread along their route, and when they return, they travel about, and thus enlarge their web.
Remedies.—These insects may be attacked in the egg or in the larval state. The former are so arranged as to be conspicuous on the naked spray at any time during the winter—whenever seen, they should be broken or cut off, and carried to the fire. In the early spring, we must watch for the little tents in the bifurcations of the limbs, and remove the nests with all the worms; this may be done when they are small, by using the thumb and finger; if larger, it is a disagreeable task, but no orchardist should hesitate when he recollects that six hundred leaves is a day's ration for one colony. They can easily be gathered in their web, thrown upon the ground, and crushed with the foot. Mr. Needham, of Massachusetts, has invented, what he calls, a caterpillar scourge; it is a little cone of wood, clothed with a piece of wool-card. This is attached to a pole: when thrust into the web, the whole nest is gathered by the card-teeth and brought down. An old dry mullein stalk has often been used for the same purpose, and some recommend burning the nest, or shooting it; but I have more faith in thumb and finger work, believing it to be more thorough.
Among the natural enemies of these caterpillars are the Tiger-beetles, which a successful orchardist of Illinois uses systematically for their destruction. He catches a beetle, and puts it upon a tree containing a nest of the Tent-caterpillar, after which he finds the worms soon disappear.
Gastrophaca Americana, (Harris).—The Lappet-caterpillars are found on apple trees. The worms are flat, and when at rest on a limb, they often escape observation from their gray color resembling the bark. A fringe of hairs, along their sides, gives them this flat appearance. They feed only at night. Dr. Harris found some in September that measured two and one-half inches in length, and above half an inch in breadth.