MANCHESTER -- Gardeners attempting to get rid of slugs could be battling with an enemy smarter than they think.

Scientists have discovered that the grey field slug appears to possess a memory, associating odours with tastes. The common garden pest also has the ability to choose a balanced diet, seeking specific foods to compensate for any dietary deficiencies, researchers at the University of Manchester and Kingston University in Surrey found.

Meanwhile, a German study at Humboldt University in Berlin showed that grey field slugs select leaves high in nitrogen content, which explains why they are attracted to well-fertilized plants, DPA reported.

Discussing the research in the BBC*** Wildlife*** magazine, gardening expert Dr. Phil Gates said the slugs were able to remember the location of young seedlings so they could return night after night until all were destroyed. He described them as "gourmets".

The grey field slug is described as a gardener's worst enemy because of the damage it can cause to a wide range of plants.

But Gates stressed that not all slugs and snails were harmful. Contrary to popular belief, some molluscs represent little threat to garden plants, and some may actually be helpful by feeding on decaying matter and fungi, he said.

Tree slugs, maug's slugs and shelled slugs are among those that are said to be potentially beneficial.