Caterpillars are the larvae of butterflies and moths. They feed voraciously on young fruit tree leaves, particularly those of apple trees. However attacks are not usually serious unless there are a lot of them.
Detecting a caterpillar attack
As ever, vigilance is the key. If you regularly inspect your fruit trees you will soon notice that something is wrong.
A typical sign of caterpillar damage is a single brown leaf, partially broken where the caterpillar has chewed through the central veins.
Another sign is a leaf, often stained brown, which has been curled up along its main axis into a cocoon. The leaf is often sealed with silk threads.
Caterpillars have natural predators, but you won't want to wait for these to turn up. It is rarely necessary to use sprays in a garden or small orchard situation, since physical removal is the best method.
Some caterpillars can cause rashes if handled, so it is often best to manouevre them off the leaf with a stick, and then stamp on them.