Adult - Garden slugs grow up to 25 to 30 mm. The mantle is on the anterior part of the slug and the breathing pore is in the anterior half of the mantle. Garden slugs have a band along either side which is not distinct on the lower border. There is no dorsal row of tubercles, and the creeping sole is yellow to dark yellow or orange. The respiratory pore is in front of the midpoint of the mantle shield. There is no keel, and the sole of foot is not divided. The skin is rough and wrinkled, gray to dark brownish gray and often with small yellow-brown dots (color lighter toward the foot). Hedgehog slugs are about 20 mm long, and are greenish to yellowish gray with one prominent dark lateral band on each side and on the mantle. The head is dark gray or black with dark gray tentacles, and the skin is covered with conical tubercles with transparent tips when contracted giving the slug a spiky appearance. The sole is yellow at the rear.

Mucus - When irritated, the slime on the body of the garden slug is yellow to dark yellow and the slime on the sole is colorless. The mucus of the hedgehog slug is golden yellow.

Young - Young garden slugs are slate gray on top. There is a dark band on each side (the band on the right enclosing the respiratory pore). The sole is yellow to orange.

Fig 139: The garden slug, Arion hortensis
The garden slug (also black field slug), Arion hortensis Ferussac; Hedgehog slug, Arion intermedius Normand, Arionidae, STYLOMMATOPHORA

Distribution - The arionid slugs are introduced from Europe. They can survive only in areas of moderate to high humidity. In the United States, arionid slugs occur naturally only in the North. Hedgehog slugs are found in the British Isles, Spain, Central Europe, and North America.

Host P1ant - The garden slug is a pest of narcissus. The hedgehog slug feeds on narcissus, grasses, lilies, (leaves, brood bulbs, flowers), and iris in greenhouses. Jimson weeds are highly favored, amaryllis (leaves, bulbs), coleus, tulip (germinating bulbs, leaves, flowers), and vegetables.

Life History - The garden slug (also called the black field slug) creeps very slowly (covers 90 cm per night) and becomes inactive at 5°C. The life span is 7.5 to 12 months and females lay 158 to 205 eggs. Garden slugs increase in size during the summer and reach sexual maturity in the autumn and winter. This slug only reproduces in the early months of the following spring. Crowding increases mortality. These slugs forage primarily from 0530 to 0600 hours although activity starts at 1900 hours. The garden slug feeds more frequently than the gray garden slug, but eats the same amount. Maximum seasonal feeding and mobility occurs in October and November. Frost and dryness drives these slugs deeper into the soil. Garden slugs reproduce faster on alkaline to neutral soils than on acid soils. The garden slug can consume 56 percent of its body weight in 1 day. Hedgehog slugs oviposit in July and August. Eggs of hedgehog slugs hatch in September and October. These new slugs mature the following spring. The life span is about 12 months.

Hedgehog slugs become infected with the ciliate, Tetrahymena rostrata (Kahl) by contact with cysts in the soil during winter. A sciomyzid fly, Tetanocera elata Meigen, parasitizes this slug in North America and Europe. Hedgehog slugs are also infected with the cestode, Davainea proglottina (Davaine).