Caterpillars are usually the larvae of moths and butterflies, but they can be mistaken for those of sawflies. Many caterpillars feed on wild plants in small numbers but others are important pests. Caterpillars feed on their hosts plants with their strong-toothed mandibles, yet the adults are not harmful as they feed on liquids, particularly nectar, sucked up through a tubular proboscis.

The adults lay clusters of eggs, usually yellow or green, on the undersides of the leaves of a food plant. The larvae of many are also familiar as either hairy or smooth, fleshy caterpillars. Sometimes the caterpillars are conspicuously coloured, but many are so well camouflaged that they are often detected by the pellets of frass (excrement) that drop from and on affected plants.

Most move around on three pairs of legs on the thorax and five pairs of prolegs. Another characteristic of caterpillars is the ability to produce silk which is often used to protect the larvae as well as the pupae, by the construction of a tent. The pupae are usually hidden in sheltered places among plants, in crevices or in the soil. Other larvae and pupae are protected inside the leaves which they have mined. 

Although most caterpillars feed on foliage, others are stem borers or live in the soil. Many of the foliage feeders are defoliators which feed voraciously on leaves, making holes and ragged edges until often only the tattered leaf skeletons are left. Among these some are leaf-tying species which feed between or inside leaves which they have fastened with silk. Some of these are webbers, colonies of which live inside a communal tent.

Among the defoliators are a number of very damaging caterpillars. One of the worst is that of the angle shades moth (Phlogophora meticulosa), a moth that has pinkish-brown wings with a central triangular band and marginal line of olive green. This caterpillar is somewhat variable in colour, from brown to dull or bright green, usually the latter predominates — all are dotted with white, with pale lines along the sides and back. Two or three generations can be found on a great variety of ornamental outdoor and glasshouse plants and many weed species, but are especially damaging to the buds and flowers of gladiolus and iris during late summer.

The caterpillars pupate in the soil in cocoons built from silk and soil. Colonies of the yellow short-haired caterpillars of the buff-tip moth (Phalera bucephala) can strip the leaves from a range of trees and bushes, including cherry, rose and viburnum, if they are not destroyed in time. As well as causing severe damage to cabbages, the greenish caterpillars of the familiar black and white cabbage white butterflies (Pieris spp.) attack a number of ornamental plants including mignonette, nasturtium and stocks.

The tomato moth (Lacanobia oleracea) can be a major pest of glasshouse carnations and chrysanthemums. The multicoloured, yellow tufted caterpillar of the vapourer moth (Orgyia antiqua) feeds on many trees and shrubs. 

There are three species of winter moths whose looper caterpillars defoliate many trees and shrubs and may injure their buds and flowers. These are the winter moth (Operophtera brumata), the March moth (Alsophila aescularia) and the mottled umber moth (Erannis defoliaria). As well as these there are several other defoliating caterpillars which are occasionally troublesome. Several caterpillars belong to species that tie the leaves of their host plants with silk. In addition to a number of other tortrix moths which injure a wide range of outdoor and glasshouse plants, the caterpillar of the carnation 

tortrix moth (Cacoecimorpha pronubana) is common outdoors on a number of shrubs but is very damaging to a range of glasshouse plants as it feeds by tunnelling into their buds and bundling leaves together. The picture to the right shows the result of tortrix moth damage to the growing tip of a disbud chrysanthemum, effectively rendering the affected lateral incapable of producing a bloom. 

As they drop from infested plants on a thread of silk if disturbed, they can easily be spread by clinging on the clothing of visitors. The caterpillars of the delphinium moth (Polychrysia moneta) which are initially brown, becoming green striped with white as they age, feed on the flowers, buds, seed capsules and leaves of delphinium, larkspur and aconitum after tying them with silk.

Tortrix moth damage to growing tip

A spray with Bifenthrin before the main caterpillar period (July August) discourages most of the moths from laying their eggs. 

Caterpillars attacking  young flowers