Gardeners attempting to get rid of slugs could be battling with an enemy smarter than they think, research has found.
Richard Cook, a senior lecturer in life sciences at Kingston University, has been working with a team at Manchester University and discovered that certain types of slugs appear to possess a memory.
The grey field slug, widely regarded as one of gardeners' worst enemies because of the damage it can cause to a range of plants, associates odours with essential food.
It is able to remember the location of nutritious young seedlings through smell and by following its slime trail and will return night after night until all plants are destroyed.
"Slugs particularly like food with high levels of nitrogen and the use of nitrogen-based fertilisers may make plants even more attractive to them," Mr Cook said.
"If they do find a rich food source they are likely to go back to it time and again, so it seems this creature is more intelligent than we thought."
The perennial pest, also the bane of farmers' lives, also has the ability to seek out a balanced diet.
Researchers monitoring slugs' eating behaviour deprived them of essential protein and carbohydrates, adding non-nutritional chemicals as flavour instead.
They compared the slugs' reaction to these samples to their response when offered protein or carbohydrate-rich food.
The slugs showed no preference for food based on taste alone but, when given a choice, selected items they detected contained the nutrients they needed.
The research could lead to the development of a new type of non-toxic slug pellet to provide a helping hand to gardeners and farmers, Mr Cook said.
"Existing pellets are full of toxins and are just as harmful to plants and crops as they are to slugs," he explained.
"If scientists can develop a non-toxic pellet full of the nutrients the slugs need, it is possible they will choose to feed on them rather than eating plants and crops."