How to recognise it
Caterpillars are the larval stage of moths and butterflies (Lepidoptera), both insects from the endopterygota group. Generally speaking caterpillars are easy to see with the naked eye; they are tubular creatures with a well developed head which contains a pair of strong mandibles for biting, a three segmented thorax, six small, jointed legs and up to a further ten ‘false’, non-jointed legs (called prolegs).
They eat plant matter and the first signs of an attack are often the defoliation of plants, although some caterpillars will be noticed through other symptoms, such as feeding in fruits or stems. A few species produce silk webbing which they attach to leaves, pulling them together to form a tent-like protective structure.
Specific symptoms are described in more detail in the information for each caterpillar type.
As part of the endopterygota group of insects, caterpillars have a complete lifecycle. Eggs are laid by the adults (butterflies or moths) which hatch within a few weeks into the larval instar, which is the caterpillar stage. The caterpillars feed for one to two months. Then they pupate, taking a few weeks to metamorphisise into the adult form. In most cases the larval stage is the only one which damages plants.
Why it’s a problem
Caterpillars eat plant life and can munch their way through leaves, stems and fruits. This can just be cosmetic damage, but in worse cases they can kill the plant or, at least, provide entry points for other pests and diseases.
Where you are likely to find it
Caterpillars can appear on almost any plant, though different species tend to prefer specific hosts. Fruit trees and bushes, vegetables such as brassicas and lettuces, roses and other trees and shrubs are particularly vulnerable. Different species will be found on different parts of the plant.
How to deter it
One of the simplest ways to prevent a caterpillar infestation is to put up barriers (such as fine netting) to prevent the adult moths and butterflies laying eggs on or around your plant (this is particularly useful in vegetable patches or cut flower production areas).
Good hygiene, particularly removing debris over the winter, can remove overwintering sites for eggs, caterpillars and pupae.
How to get rid of it
Regular inspections of susceptible plants will enable you to pick off and dispose of any caterpillars or eggs on the plant. This method may seem a bit basic, but it works more quickly and effectively than insecticides.
Encouraging natural predators into your garden, such as birds and predaceous insects can help to control the population, although they may bring different pest problems into your garden.
Contact insecticides are available to kill caterpillars, although you must be careful to get the right chemical for the type of caterpillar you have and the type of plant being attacked. Some systemic insecticides also treat caterpillars (if they have some residual contact action), although they are less effective on caterpillars than other pests such as aphids.
A biological control, Bacillus thuringiensis, is available for leaf-feeding caterpillars, particularly those attacking brassicas.
Is it good for anything?!
Yes; moths and butterflies are beautiful additions to any garden. They only feed on sugary substances such as nectar (or they don’t feed at all) so do no damage to your plants.
Other useful information
We have more information on the following caterpillars: