Slug (limax, Lam.), a genus of mollusk, belonging to the air-breathing gasteropods. The form is elongated, tapering, snail-like, the head having two long and two short tentacles which can be extended and drawn in like the finger of a glove by being turned inside and out; the naked body is covered anteriorly by a coriaceous mantle, under which is the branchial cavity, the respiratory orifice and vent opening on the right side of it, and the generative orifice beneath the right tentacles; the mantle in some contains a calcareous grit, and in others a small, thin, nail-like shell; the head can be partly drawn under the mantle; at the posterior end of the body is a small aperture whence proceed the adhesive threads by which they let themselves down from plants which they ascend in search of food. Their motion is proverbially slow, and effected by the contractions of the flat disk or foot on the ventral surface. The upper jaw is in the form of a toothed crescent, by which they gnaw plants with great voracity; the stomach is elongated; the skin secretes a great quantity of mucosity, which serves to attach them to the surfaces on which they creep; the eyes are small black disks at the end of the posterior tentacles; the sense of touch is delicate.

The reproductive season is in spring and summer; they are hermaphrodite, and mutually impregnate each other; the eggs, to the number of 700 or 800, are laid in moist and shady places; at the approach of winter they burrow into the ground, where they hibernate; they hide under decaying logs and stones in damp places, and are seen in gardens and orchards in evening and early morning, especially after gentle and warm showers. They are found in the northern temperate zones of both hemispheres. The common slug of New England, L. tunicata (Gould), is nearly an inch long, varying in color from dark drab to blackish brown; the back is wrinkled, and the upper tentacles granulated and black at the tips; the foot is very narrow; it is found almost always with the isopod crustaceans commonly called sow bugs. Other species are described; they are comparatively rare in the United States, and by no means so troublesome as in Europe. The common European slug, L. agrestis (Linn.), is small and unspotted, and very abundant and destructive; they are killed by solutions of tobacco, salt, or other irritants, or by covering a spot infested by them with ashes, lime, line sand, or any powder which attaches itself to the body and prevents their walking, or they may be arrested by some sticky substance; many are devoured by mammals, birds, and reptiles.

SLUG WORM, the common name of the larvae of the sawflies, or the hymcnopterous insects of the family tentliredinidoe. The slug worm described by Prof. Peck in his prize essay (Boston, 1799), and called by him tenthredo cerasi (Linn.), has been placed by Harris in the genus Selandria (blennocampa). The fly is black, with the first pair of legs yellowish clay-colored; the body of the female is about a fifth of an inch long, that of the male a little smaller. They usually appear in Massachusetts on the cherry and plum trees toward the end of May, disappearing in three weeks after laying their eggs singly in incisions on the lower surface of the leaves; the young are hatched in two weeks, coming out from June 5 to July 20, according to season; they have 20 short legs, a pair under every segment except the fourth and the last, and are half an inch long when fully grown; in form they resemble small tadpoles, and are covered with a thick slimy matter which has given them the name of slugs; they also emit a disagreeable odor.

They come to their full size in 26 days, casting their skin five times, after which they enter the ground, change to chrysalids, and come out flies in 16 days; they then lay eggs for a second brood, which enter the ground in autumn, and appear as flies in the ensuing spring, some remaining unchanged for a year longer. They feed on leaves, and in some seasons have been so numerous as to strip trees entirely of their foliage and even cause their destruction; they are eaten by small mammals and birds, and the eggs are destroyed by the larvae of a tiny ichneumon fly (encyrtus). The trees may be best preserved against their attacks by showering them with a mixture of whale-oil soap and water, or powdering with ashes or quicklime.

Slug (Limax agrestis).

Slug (Limax agrestis).