AbstractThe pond snailLymnaea stagnaliswas fed on maize pellets containing metaldehyde. With increasing concentration of metaldehyde there was a decrease in the meal length, number of bites per meal and amount of pellet eaten. The irregularity of biting and the amount of time spent pausing during the meal increased.Meals on maize pellets in the presence of acetaldehyde (one of the metabolites of metaldehyde) were shorter than control meals on maize pellets alone.The symptoms of poisoning after ingestion of metaldehyde or in the presence of acetaldehyde were similar. There was an increase in mucus secretion. Animals showed muscular spasms, undirected mouthing movements and uncoordinated locomotion. This was followed by a period of immobility.The isolated central nervous system ofL. stagnaliswas used to study the effects of metaldehyde and acetaldehyde on the neural activity underlying feeding. Application of metaldehyde or acetaldehyde led to an increase in firing activity and development of paroxysmal depolarising shifts in buccal motoneurons. It is argued that this type of activity could explain some of the symptoms of poisoning seen in the whole animal after ingestion of metaldehyde, and that acetaldehyde may be responsible for some of the toxic effects of metaldehyde.These results suggest that the CNS ofL. stagnalisprovides a useful model for screening molluscicides for their effects on a functional neuronal network.