The adult slug is familiar to most gardeners! They come in a range of sizes and colours depending on the species.
The field slug is small (2cm) and grey, while the round back slugs can be relatively large (5-10cm) and black or brown in colour. in some cases round black slugs can have vibrant orange colouring on their foot.
Slugs are capable of feeding on flowers, leaves, stems, roots and seeds.
Leaf damage is usually shown as leaf shredding or severe notching.
Young plants are most at risk as the leaf feeding can be so severe that the plants die.
A Hosta with extensive slug damage
What is seen less often is the damage they cause below the soil surface to seeds, roots etc. This damage can result in seed that does not germinate, and in the case of potatoes, a very poor and damaged crop (see picture above).
Slug Life Cycle
Slugs are hermaphrodite, so every individual can lay eggs – up to 300 each slug. Eggs are laid in batches, usually 10-50, in moist but not waterlogged soil.
Most species found in gardens have an annual life cycle lasting less than a year, and lay eggs in any month providing conditions are suitable.
For example, field slugs hatching from eggs laid in the spring will become adults and lay eggs in the autumn. Eggs laid in the autumn will develop into adults the following summer. Because its generations overlap, all stages of the field slug are present throughout the year.
Many slugs spend most of their life below the soil surface tunnelling, rather like earthworms. Those seen on the soil surface represent only a small part of the total slug population.
They have a remarkable ability to survive during dry and cold periods by remaining deep in the soil.
Biological Control of Slugs
Slugs can be controlled biologically by using their natural enemy, the nematode Phasmarhabditis also known as Nemaslug.