Invertebrates cause damage to leaves and in turn reduce the yield and vigour of the crop. Invertebrates that attack crops are commonly one of the following:

• molluscs - slugs and snails
• nematodes - microscopic worms, some of which can establish as parasites
• herbivorous insects - for example aphids

Some invertebrate pests can also carry plant diseases that can be caused by fungi, bacteria or viruses that lower crop yield and productivity.