Terrestrial slugs ( Gastropoda Pulmonata) are molluscs which lack a large external shell, having instead a shell beneath their skin (or the remnants there of). They breath through a mantle cavity, and have eye bearing tentacles at the front of their body. Slugs move on a muscular foot over a mucus trail produced by a pedal mucus gland.

They may follow these slime trails from their previous excursions, and other slugs can also pick up on them, creating slug networks to host plants. Slugs are hermaphrodites, possessing both male and female reproductive systems. Eggs are laid in clusters of two dozen eggs which may lie dormant in the soil until conditions are right, since they require moisture to hatch. The adults also over-winter in the soil and can live for many years, dependent on species.

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Although a large number of different species of slug are found in agricultural crops, the majority of the damage is caused by the field slug Deroceras reticulatum (left), and to a lesser extent Arion spp. and milacid slugs.

The pictures below show the damage done by slugs to potatoes (left) and radishes (right), and D. reticulatum attacking lettuce (middle).

Slugs have a large number of predators, including parasitic nematodes. The most popular method for dealing with them is chemical pellets, either metaldehyde or, more common in agriculture methiocarb (3,5-dimethyl-4- (methylthio) phenyl methylcarbamate C11H15NO2S) based. These have a number of problems, and are clearly not suitable for organic farming. Even in conventional farming, most European countries have a minimum time after application before crops are allowed to be harvested. In addition to slugs and snails, pellets kill many natural predators of slugs such as birds, beetles, hedgehogs, as well as pets(cats, dogs, tortoises etc). This may be either by directly eating pellets (dogs can become addicted to the pellets), or through consuming poisoned slugs. In fact, some researchers have considered methiocarb to control problem bird populations, and the Ministry of Agiiculture once advised the use of slug pellets for the control of small mammals on farms. Chemical treatments are also often highly susceptible to rain, and get washed away. This not only makes them ineffectual against slugs, but results in the pollution of rivers and other areas.

There are however numerous of other ways of dealing with them, including encouraging natural predators such as frogs, birds, hedgehogs and beetles. In a gardening context, there are many things you can do - lots of useful information is given on Dr Bill Symondson's Slug Control page. Pro-active controls (apart from the nematodes considered here) which do not harm the environment include beer traps, barrier tape and barrier paste.

There are numerous Slug Sites - both for and against them! Below are a selection of the most informative or bio-control biased ones, or particularly good jump stations. Please feel free to contact us if there are any sites you think should be added.

Australian Museum online malacology section: "Great websites for Mollusc information". Lots of links to many informative sites.

Internet Resource Guide for Zoology from BIOSIS and the Zoological Society of London. Links to scientific and technical sites, including more general mollusca.

Institut National de la Recherche Agronomique. A comprehensive website on the zoology of slugs, including detailed information on individual species.

Dr Bill Symondson's Slug Control page, offering invaluable advice on ways to deal with slugs in your garden.

The Crop Ecology and Management Group, Long Ashton Research Station (part of The Institute of Arable Crop Research). Lots of interesting research on, among other things, slug control. The groups is concerned with less intensive integrated crop management, modelling effects of climate change on crops, population dynamics and biological and integrated control of slugs.

Novel technologies for integrated control of slug damage in key horticultural crops. A European Union funded research project at Long Ashton Research Station (part of The Institute of Arable Crop Research).

Golden Harvest Organics. Slug and slug control information including organic crop protection products.

Slug Web - not a huge amount of information but much devotion to the mascot of the University of California at Santa Cruz - perhaps even enough to make us all appreciate slugs a little more!