Lehmannis Slugs

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SLUGS AND SNAILS
Lehmannia Slugs

DESCRIPTION

Adult - Lehmannia poirieri is a light brown to yellowish gray slug with dark lines along the top of the body. There is a pair of faint grooves just above the foot. The mantle does not have a groove or fold although it is faintly concentrically wrinkled. When irritated, the mucus secreted is colorless. This slug grows to about 60 mm long and can stretch to about 75 mm.

The tree slug, Lehmannia marginata (Muller), is a gray to reddish slug with a lighter median stripe down the back. It usually has a large, translucent water reservoir (body) at the tail. The respiratory pore is behind the middle of the mantle, and the body is keeled only at tail. The mantle is 1/3 of the body length just behind the head. Each side has two dark bands lengthwise (lower band sometimes forming a network, and often faint). The mantle has three dark, lengthwise bands (median faint) and the pale areas between the bands forming a lyre shape. The sole is gray, often with a darker median area. The mucus is colorless and watery.

Egg - The eggs of the tree slug are oval to somewhat pointed on one end. The eggs tend to be opaque when first laid and become more transparent as the embryo develops. The surface of the eggs is covered by tiny wavy wrinkles. The size of the eggs may vary from one slug to the next although the eggs in one clutch (up to 63 eggs per clutch) are fairly uniform (2 to 2.5 mm).

Young - No description found.

Fig 143 Lehmannia slug. Lehmannia poirieri (Mabille)(= Limax marginatus of Pilsbry); tree slug, Lehmannia marginatus (O. M. Muller) (= Limax arborum Bouchard-Chantereaux), Limacidae, STYLOMMATOPHORA

BIOLOGY

Distribution - There is some confusion in the literature about the identity of Lehmannia poirieri. In the American literature this slug was at one time called Limax marginatus. There is now an old world slug called Lehmannia marginatus (Muller), the tree slug, which is apparently similar to if not the same species as Lehmannia poirieri. However, the tree is an arboreal slug in Europe whereas Lehmannia poirieri seems to be terrestrial in the United States. It is thought that

Lehmannia poirieri was introduced from Europe and now occurs throughout the United States where it tends to occur around dwellings, greenhouses, and gardens. In Europe, the tree slug inhabits woodlands and damp rocks on open hillsides. The tree slug is found in England, Europe, Australia, Japan, Mexico, and Venezuela.

Host Plants - Lehmannia poirieri feeds readily on living plant material and has been associated with damage to pepper plants, carnation, ivy, vinca, and Cymbidium. Tree slugs feed on hosta, vegetables, wheat, jimson weed, and usually prefer vegetable diet to casein or blood meal. In the greenhouse it feeds on amaryllis, asters, mums, orchids, and Tradescantia.

Damage - Aside from the direct damage Lehmannia poirieri does to bedding plants and vegetables, this slug (or a very closely related species) has been found to be an intermediate host of a parasitic nematode of rats. Slugs have been implicated as intermediate hosts of the fowl tapeworm, Davainea proglottina (for this reason it is suggested slugs not be eaten raw). The tree slug can transmit tobacco mosaic virus.

Life History - Lehmannia slugs require a higher moisture substrate than other limacid slugs. Lehmannia poirieri also tends to burrow into soft soil. During the day this slug tends to rest under boards, logs, flats, and other debris. Lehmannia slugs space themselves so they do not touch in the daytime resting sites in summer, but cluster tightly during the winter. Lehmannia slugs have an elaborate courtship behavior which lasts from a half to 2 hours. Eggs are laid sometime later (perhaps many weeks later). Young slugs hatch from the eggs about 2 weeks later at 68°F. Tree slugs live 24 to 26 months, and lay 105 to 132 eggs. This slug searches the edges of strange environments and can learn the position of food.

CONTROL

Tree slugs are infected with the sporozoan, Pfeifferinela impudica Leger & Hollande, and with the ciliates, Colpoda steini Maupas, Tetrahymena limacis (Warren), and Tetrahymena rostrata (Kahl) that infect this slug during the winter probably from cysts in the soil. The trematode, Strongylus spp. has been found in eggs of tree slugs. The trombidiid mite, Riccardoella limacum (Schrank), can considerably reduce a slug population especially in captivity. The mites crawl rapidly on the surface of the slug and disappear into the respiratory pore when mites are disturbed.

Tree slugs are intermediate in resistance to molluscicides. Tree slugs habituate to the attractiveness of metaldehyde so that broadcasting of baits tends to give better control than clumps. When sprayed, these slugs crawl onto each other to avoid the residue. Metaldehyde only gives 35 percent mortality if the weather is cool and rainy. Moisture does not seem to improve the efficacy of carbamates for tree slug management. One method of controlling Lehmannia poirieri is removal of its hiding places. Picking up flats, boards, pots, and debris will force the slugs to crawl elsewhere for a suitable resting spot. For specific chemical control recommendations, see the current Cooperative Extension publications on ornamental plant pest management or consult your county Extension agent.

Reference to University of Florida/IFAS Pest Control Guides