Vapourer moth caterpillars on laurel
Caterpillars are the larvae of butterflies and moths. Typically, caterpillars feed on the shoots and leaves of plants for a few weeks before pupating in the soil, or in a dry place, and emerge as adults some weeks later, or the following spring. They vary considerably in size. Some are only a fraction of an inch long; others can reach 7.5 centimetres.
Caterpillar damage is easily recognised – irregular holes of various sizes, often bounded by leaf veins. The holes will have traces of caterpillar droppings, by contrast with slug damage which has slime trails.
Some kinds of caterpillar burrow into plant tissues, such as heads of cabbage and cauliflower. Practically every plant – trees, flowers, fruit or vegetables – has its own caterpillar pest, but they usually do not cause damage serious enough to warrant control measures.
Cabbage caterpillars are the major exception – they almost always cause considerable damage. Caterpillars can be picked or knocked off the plants, and killed. Batches of yellow or white eggs, often visible on the undersides of leaves, can be destroyed. If small holes appear on houseplants, a careful search may uncover a single, small caterpillar which can then be removed.
Chemical control is not usually necessary, except on the cabbage family. Suitable insecticides include a general garden insecticide or Caterpillar Spray.