Swallowtail Butterfly Caterpillar – Photo by Angelo Eliades

Caterpillars are the larval stage of butterflies and moths, and at this stage of their life cycle they are a major garden pest on many fruits and vegetables, ornamental plants and shade trees. They are normally hairless, with a long, soft, segmented cylindrical body around 10mm to 50mm in length and vary in colour. There are some ‘hairy’ caterpillars whose protective hairs can cause urticaria (skin rash and itching) in sensitive people. Most pest caterpillars are moth larvae, there are much lest pest butterflies overall.

You can distinguish caterpillars from larvae of other insects such as those beetles, flies and sawflies by their appearance – caterpillars have three pairs of legs directly behind the head, and fleshy, false leg-like appendages on some but not all of the rear segments of the abdomen,

Pest Life Cycle

Eggs are usually laid on the underside of leaves, either singly or in clusters, and these hatch into caterpillars a few days later.  Newly emerged caterpillars feed for two to three weeks, growing in size and creating considerable plant damage in the process. They then build a cocoon in which they undergo metamorphosis, transforming into adults, emerging to lay more eggs.

Caterpillar Damage

Different types of caterpillar may damage plants in various ways. The ones we’re most familiar with eat leaves, either eating away at the leaf edges or chewing large ragged holes through the leaf, leaving the large veins and midrib intact.

One tell-tale sign of caterpillars is the large amounts of dark green frass (caterpillar excrement) left behind on the leaves directly below where they have been feeding.

Caterpillars are difficult to locate as they often hide on the underside of leaves and lie along leaf veins or the midrib of the leaf to disguise their presence.

It’s important to note that not all caterpillars eat leaves, some attack and damage stems, flowers, shoots and roots, while others tunnel into fruit.

Identifying Common Pest Caterpillars

Many of these pest caterpillars can be identified by their characteristic appearance, the damage which they cause and the plants that they commonly attack. By correctly identifying a pest, we can choose the most effective pest control measures.

The common green caterpillars of the large cabbage white butterfly are easy to identify. The mature larvae are about 30mm long, and the eggs which are laid on the leaf undersides, are oblong (football-shape standing on one end), and white to cream coloured, eventually turning yellowish.

The adult diamond-back moth is quite small, only about 10-12 mm long. The male moth is dark brown in colour and has three white diamond-shapes in a line along its back. The female is tan in colour and the diamond shapes are less distinct compared to the male’s markings.

Their eggs are pale yellow in colour, oval and flattened, and around 0.5 mm long. The caterpillar has four growth stages, being grey-green with a dark head in the first three stages and changing into a green colour with a green-brown head in the final stage, growing to approximately 12 mm in length

Being quite small, these caterpillars eat many small holes in leaves, often eating only part way through the layers of the leaf and leaving a ‘window’ of the leaf epidermis (the outermost layer of cells) intact.

The cabbage white butterfly and the diamond-back (cabbage) moth are major pests of brassica crops, severely damaging the leaves.

Cluster caterpillars and looper caterpillars are also leaf eaters and will attack the leaves of many vegetables.

Cluster caterpillars are named as such because the young caterpillars can be found feeding in large groups together, though they become solitary as they mature. They eat the underside of the leaf surface, leaving the top surface intact, creating a ‘window effect’ on the leaf. The young cluster caterpillars are translucent green on colour with black heads, and when mature have a distinctive marking of line of black triangles running along each side of their body.

Eggs are laid in on leaves large clusters of up to 300 and are covered with a layer of grey-brown hairs from the body of the female moth.

The adult moths are around 16 mm in length, greyish-brown in colour with silvery marbling on their forewings, while their hind-wings are translucent white.

Looper caterpillars are a large family of caterpillars that earn their name because of the way they move with a characteristic looping motion, forming a horseshoe shaped loop then stretching out. They sometimes disguise themselves as twigs.

The grapevine moth caterpillar is a pest of grape vine plants, and it attacks both the leaves and developing fruit. It will also eat Fuchsias, Evening Primroses and the native Hibbertia obtusifolia (hoary Guinea-flower). This caterpillar has a striking appearance, its black body is covered with pale yellow lines running across and along its body in a checkered pattern. Its body is covered in scattered white hairs, it has a light brown head, a series of lateral red spots, a bright red band near the rear and it can reach a length of 50mm.

The adult grapevine moth is a day-flying moth, with a wingspan of up to 50mm. The wings are black with striking white bands on the forewings, and a white outer margin on the hindwings. The abdomen is black on top and has orange stripes underneath. The body has tufts of bright red hair on the tip of the abdomen, and at the bases of the legs. These red hairs extend out and are visible from above.

Similarly, the light brown apple moth, which attacks both leaves and fruit, is serious pest of pome fruit, grapevines, and other crops. This caterpillar attacks fruit crops, broad-leaved weeds, ornamental plants and some vegetables.

The adult light brown apple moth is about 10mm long, yellowish-brown in colour, though this can vary, and its forewings have darker brown markings on them. When resting with wings folded its body forms a characteristic bell shape.  During the day these moths hide amongst foliage, and if disturbed, will take off in short erratic flights.

The light brown apple moth lays its eggs in masses on the upper leaf surface of smooth-leaved plants. The newly hatched caterpillars are very tiny in size, pale yellow-green in colour with a pale brown head. Fully grown, they will reach 10 to 15 mm in length and about 1.4 mm wide at their head.

What makes them easy to identify is that they hide on the underside of leaves and cover themselves with a protective fine webbing and then start feeding alongside a leaf vein. When they’re not hiding they will actively wander actively over plant surfaces. These caterpillars are often seen hanging down from a fine silk thread lowering themselves to a location where they can feed, a sight many gardeners are familiar with.

As the caterpillars grow they’ll join two leaves together or a leaf to a fruit with their protective web and feed from there. They will also weave their protective web in the centre of a cluster of fruit. They will wriggle aggressively if disturbed and either retreat into their protective webs or fall to the ground to escape.

Some caterpillars bore into fruit, making them hard to kill. The only measures are preventative ones such as traps or early spraying to kill them before they get inside the fruit.

Fruit growers will be familiar with the codling moth, which is a major pest of pome fruit such as apples, pears. They also may attack quinces and walnuts, but this is less common. The newly hatched caterpillars chew through fruit and tunnel their way into to the core. The characteristic sign of codling moth is one or more holes in a fruit that are blocked with frass (caterpillar excrement) and may also be exuding a sticky, syrupy substance as the fruit matures. Similar damage can be caused by the oriental fruit moth when pome fruit is grown near stone fruit, as this moth attacks the young shoots and fruit of stone fruit but apples, pears and quinces may also be damaged.

The newly-hatched codling moth caterpillars are white with a black head, and when fully mature they are a creamy pink colour with a dark brown head, and reach a length of around 15mm.

Eggs are laid singly on leaves and fruit, are flat and oval in shape and around 1 mm long. Their colour is opaque white when first laid but as they mature they develop a red ring, and just before hatching, the black heads of the caterpillars becomes visible in the egg.

The adult codling moth is a small moth about 10 mm long, with the males being smaller than the females. Their forewings are brownish grey in colour with several grey cross-line markings and an iridescent coppery-brown spot is present near the tip, while the hind wings are pale grey with fringed borders.

The egg fruit caterpillar bores into eggplant fruit but it also occasionally attacks tomato, capsicum and pepino fruit. The damage caused by this caterpillar It is not apparent until either the mature caterpillar tunnels out, leaving a 3-4mm exit hole, or when the fruit is harvested and cut open. These caterpillars burrow into the centre of the fruit and feed on the developing seeds.

The young caterpillars are creamy-white in colour, and when they mature they become pink in colour and grow to a length of around 20 mm.

Eggs are laid mainly on the calyx of the fruit, are small and flattened with a low longitudinal ridge, initially whitish in colour, the eggs turn red after 1-2 days.

The adult eggfruit caterpillar moths have distinctive yellowish-brown patterned wings triangular wings with a 25mm wingspan and they characteristically sit at rest with the abdomen curled upwards.

The native budworm is the major pest of all grain legumes such as beans and chickpeas, but they will also bore into the fruit of many vegetables, especially capsicums, tomatoes and sweet corn. In addition, they will also attack sunflowers.

The newly hatched caterpillars are about 1.5 mm long with dark brown heads and white bodies, growing to a size of 35 to 40 mm long. When mature, their colour changes, and can range from green, yellow, buff, red or brown to almost black.  Their identifying markings are a broad yellow-white stripe down each side of the body and a dark stripe down the centre of the back, as well as the prominent bumps on the body with long, dark sparse hairs.

Eggs are laid singly on buds and growing tips of plants. They are very small, about 0.5 mm in diameter, but are quite visible as they are white in colour when first laid, but as they get closer to hatching they change colour to yellow and brown.

The adult budworm moths are stout-bodied medium sized insects with a wingspan of 30-40mm. The colour of the forewings is light brown and patterned, though it may vary from buff-olive to red-brown. The hind wings are mostly pale with distinctive dark bands on the bottom edge.

 

Some caterpillars attack the roots and stems of plants. The potato moth caterpillar will ‘mine’ potato leaves and bore into potato tubers. It also infests other plants of the Solanum family such as tomato and pepino, as well as weeds from this family such as nightshades and thornapple.

This caterpillar grows to around 12 mm long and has a dark head with a greyish-pink body if it is feeding in a tuber or is dark green if it feeds on leaves. It only crawls over leaves a short time before it mines into them, between the upper and lower layers of the leaf.

The areas inside the leaf that have been eaten-out area become brown and brittle, with particles of frass (caterpillar excrement) enclosed in the blister where the caterpillar resides. As the caterpillar grows it eat into the leaf stalk or stem, which usually kills that terminal section of the plant. When feeding on tubers, the caterpillars will tunnel just below the surface to begin with but will them tunnel more deeply later on.

This moth lays its tiny white eggs singly on the undersides of leaves, or in groups around the eyes or surface scars of tubers.

The adult potato moth has a wingspan of about 12 mm, with brownish grey forewings with tiny dark scattered markings. The hind wings are pale-cream in colour with a fringe of fine hairs on their borders.

There are several species of cutworms, but as their name suggests, they all hide in the soil by day and attack the stems of young seedlings at night, severing them at or near ground level.

These caterpillars are up to 50 mm in length. They have dark heads and their bodies are hairless, usually darkish in colour, often with longitudinal lines and/or dark spots., If picked up or disturbed, cutworm caterpillars curl up and remain still.

Cutworms feeding in the late afternoon or at night, and hide under debris or in the soil during the day. Young caterpillars will climb plants and eat small holes in leaves or skeletonise them completely. Older caterpillars can also climb to eat leaves, but prefer to cut through stems of seedlings at ground level and eat the top growth of plants they cut down. Mature caterpillars often remain underground and chew into plants at or below ground level

These moths prefer to lay their eggs in the soil, either in areas of bare soil or areas that lightly vegetated, such as weed patches. The adult moths are a dull brown-black colour.

There’s also a caterpillar which attacks cereal crops and most lawn grasses. The lawn armyworm will strip leaves up to 45 cm from ground level. They breed up in large numbers and will eat away large patches of lawn and also leave grass leaves on the top of the lawn which have been cut off at the base. They’re called “armyworms” because they will march out of crops and pastures like an army, in huge numbers, in search of more food if they become overcrowded or encounter extreme food depletion.

The newly hatched caterpillars start off cream coloured but become a greenish colour after they begin feeding. As they grow, they develop characteristic thin white stripes running lengthwise on the sides and top of the body, making them relatively easy to identify, and their head changes from black to brown in colour. As they mature, the caterpillars become brown with two rows of black triangular marks down their back.

The lawn armyworm caterpillars grow up to 45 mm in length and 7 mm thick, with the body wider than the head giving an inflated appearance.  They have three pairs of walking legs on the front of the body and five pairs of fleshy leg-like appendages on the rear. If disturbed, they curl into a tight spiral to protect themselves.

The eggs are laid in clusters which are covered with fine scales on both the upper and lower surfaces of the leaves of trees and plants that they don’t eat, usually within a few metres of the ground, and also on object such as walls or under the eaves of buildings. The leaves of trees such as citrus, eucalypt and papaya are favoured backyard egg laying locations. Each individual egg is about 0.5mm wide, shaped like a flattened globe and light brown in colour. A single egg mass can contain three to six layers of eggs.

The adult lawn armyworm is a greyish-brown moth with a complex pattern of light marks on the forewings. The hindwings are a pale, shining white or pearly white colour. It has a wingspan of 35 to 40 mm. and the wings are folded over the body when the moth is at rest.

Conclusion

The first step in any pest control plan is to correctly identify the pest, this allows us to select the most appropriate control measures.

As we can see, there are a wide variety of caterpillars which attack plants, each having a distinct appearance and leaving its own characteristic plant damage signature.

With correct pest identification, a gardener can save time, money and cause the least damage to the environment in the process.

Images of all the pests described are available in the links in the reference section below, along with lots of other useful additional information. The references are drawn from various government departments and university agricultural extension services which provide authoritative information on pest identification and control for both agriculture and backyard gardens.

References:

  1. ‘Main Insect Pests of Vegetables in Home Gardens’ – Department of Agriculture and Food, Western Australia, Gardennote No 359, John Burt, Horticulture, Harald Hoffmann, Biosecurity Communications, Darryl Hardie, Entomology and Hossein Golzar, Plant Pathology, South Perth.
  2. ‘Vegetable Insects, Managing Insects in The Home Vegetable Garden’ – Purdue University Cooperative Extension Service, Rick E. Foster and John Obermeyer, Extension Entomologists
  3. ‘Insect Pests of Vegetables’ – Department of Agriculture and Food, Western Australia
  4. ‘Caterpillars’ – University of California Agriculture and Natural Resources, Statewide Integrated Pest Management Program
  5. Diamondback Moth – Agriculture Victoria, Note Number: AG0512, Nancy Endersby and Peter Ridland, Knoxfield
  6. ‘Diamondback Moth’ – Queensland Department of Agriculture and Fisheries, A-Z list of horticultural insect pests
  7. Codling Moth – Agriculture Victoria, Note Number: AG0095, David Williams, Knoxfield
  8. Codling Moth – University of California Agriculture and Natural Resources, Statewide Integrated Pest Management Program
  9. Eggfruit caterpillar – Queensland Government, Department of Agriculture and Fisheries
  10. Potato moth– Queensland Department of Agriculture and Fisheries, A-Z list of horticultural insect pests
  11. Armyworms – Agriculture Victoria, Note Number: AG0412, Published: June 1995. Garry McDonald, La Trobe University