Caterpillars

Garden pest

Description

Caterpillars are the larval stage of butterflies and moths, not a single species. Many feed on garden plants, although some species are harmless or valued as future pollinators. Their appearance varies widely: they may be green, brown, striped, spotted, smooth, or hairy. Most chew leaves, making small holes or ragged edges; heavy feeding can strip a plant of foliage. Some roll leaves together with silk or feed inside stems and fruit, where they are harder to see. Fresh, pellet-like droppings, called frass, often collect below feeding sites or near an entrance hole. Damage depends on the species and the plant’s size: an established plant may tolerate a few caterpillars, while seedlings can be badly damaged overnight. Caterpillars occur throughout the growing season wherever adult moths or butterflies lay eggs. Identification matters because a few caterpillars can usually be managed without treating the whole garden.

Symptoms

• Holes in leaves
• Insects visible on the plant
• Stems chewed or cut through
• Wilting
• Stunted growth
• Rotting fruit

How to Identify

Look for soft-bodied larvae on leaves, especially their undersides, and check nearby for dark, pellet-like frass. Search at dusk or at night if damage appears but no pest is visible. Rolled or silk-tied leaves may conceal a caterpillar; a small hole and frass on fruit or stems can indicate one feeding inside. Unlike slugs and snails, caterpillars do not leave slime trails. Beetles generally have a harder, more clearly segmented body. Sawfly larvae can look similar, but most have six or more pairs of fleshy abdominal legs; most caterpillars have two to five pairs. Identify the species before removing larvae from butterfly host plants.

Prevention

Inspect plants regularly, especially seedlings and the undersides of leaves, so eggs and young caterpillars are found before feeding becomes extensive. Remove weeds and crop debris that shelter pests, and rotate vegetable crops where practical. Cover susceptible crops with fine insect mesh before adults lay eggs; secure the edges and check underneath for insects already present. Remove covers from crops that need insect pollination during flowering, or hand-pollinate them. Keep plants healthy with appropriate water and spacing so they can better tolerate minor leaf loss. Where space allows, grow extra host plants for butterflies rather than treating every caterpillar. Avoid routine broad-spectrum insecticide use: it can kill beneficial insects that prey on or parasitize caterpillars.

Treatment

If damage is light, leave the caterpillars alone or move them to a suitable spare host plant. Otherwise, hand-pick visible larvae and egg clusters, wearing gloves if larvae are hairy or irritating. Open rolled leaves to find hidden feeders, and remove badly infested leaves or fruit; dispose of material containing larvae. Protect young plants with insect mesh after checking that no caterpillars remain beneath it. For persistent feeding by exposed caterpillars, consider a product containing Bacillus thuringiensis subsp. kurstaki (Bt); young larvae must eat treated foliage for it to work. Follow the label, and avoid spraying plants used by butterflies you want to protect. Spinosad is another option where labeled for the crop and pest, but it can harm beneficial insects: use it only if simpler measures fail, and follow label precautions for pollinators. Caterpillars feeding deep inside stems or fruit are difficult to reach; remove affected parts promptly.

Plants Affected

Bigtooth Aspen, Black Cherry, Black Oak, Black Walnut, Bougainvillea, Boxwood, Broom, Bur Oak, Buxus, Catalpa, Chestnut Oak, Chestnut-leaved Oak, Chinkapin Oak, Chokecherry, Cork Oak, Corn, Dill, Douglas Fir, Drumstick, Glutinous Rice, Holm Oak, Indica Rice, Larch, Lindera, Live Oak, Northern Catalpa, Oak, Oil Palm, Oleander, Parsley, Passionflower, Pecan, Petunia, Pin Cherry, Poncirus, Post Oak, Queen Anne’s Lace, River Red Gum, Royal Palm, Sandalwood, Shagbark Hickory, Southern Catalpa, Sushi Rice, Swamp Chestnut Oak, Tamarind, Teak, Thuja, White Oak, Yellow Birch

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