Plant it, and they will come. Lettuce, kale, sweet potato - all fair game for the slugs in the backyard. The arugula seems like the only thing they won't touch, but that's probably because they're too busy eating the rest of the garden goodies (even slugs have preferences). So if you can't beat 'em, my tactic is to learn more about them.
First off, they are gastropods, a class of animals that translates into "stomach-foot," and though it may appear that they slide along on their bellies, their digestive system is actually in a hump located on the backside, or dorsal side of their bodies. Unlike their other gastropod relatives, the snails, there is no shell, or there may be a reduced or internal shell. There are sea slugs, and even a genus of freshwater slugs, but in general usage, the term "slug" refers to land slugs, of which Hawaii has several species. Slugs need damp places to keep their soft bodies from drying out, so they tend to be nocturnal, when they can go about eating without worrying about dessication. They secrete two types of mucus: one that is thin and slippery, and another that is thick and sticky. The mucus serves several functions: it helps them to glide with little friction, but also keeps them from falling off of vertical surfaces. It also slows water loss, and presents potential predators with a slippery and distasteful surface that may be hard to hold onto. The all-too-familiar slime trail left by slugs may also serve as a mode of communication among slugs seeking a mate, but on the flip side, it may clue carnivorous snails to the location of their next meal.
Land slugs are hermaphrodites, meaning each slug has male and female reproductive parts. Mating is a two-for-one special, with slugs exchanging sperm, then off they both go, laying (typically) about thirty eggs a few days later. The young hatch within a month, looking to see what's new in your garden. Like the adults, the young have two pairs of tentacles: the longer top pair are optical, with eyespots at the ends, and the shorter pair are for smell and touch. Respiration is often accomplished through the skin and through a hole in the top side of the slug called a pnuemostome, which is hard to see when it is closed.
Some of the slugs seen here in Hawaii include: Sarasinula plebeia (the bean slug), Veronicella cubensis (the cuban slug), and Parmarion martensi (the yellow-shelled semislug). Some slugs and snails can be intermediate hosts of rat lungworm, a roundworm that can cause eosinophilic meningitis. The slugs pick up the larvae of the roundworm by ingesting rat feces; the larvae are then transferred to humans through vegetable matter eaten by the slugs, or by consuming the slugs themselves. It is essential that care is taken to wash any greens from your garden. With all that being said, slugs do have ecological benefits: they are an important food source for many animals, and help in the recycling of nutrients by breaking down organic matter.
The Yellow-shelled semislug, Parmarion martensi, and according to Wikipedia, it "is a host for the nematode Angiostrongylus cantonensis, which causes rat lungworm disease. Parmarion martensi feeds on lettuce and on papaya in gardens in Hawaii, and is considered to be a pest." Photo: Forest and Kim Starr.
welcomes you to visit with the all the wonderful flora and fauna that we share this lovely aina with.