Caterpillars Are Eating My Pansies and Violas: What Should I Do?

Finding large, ragged holes in pansy and viola foliage with no apparent pest visible during the day is a classic sign of caterpillar feeding. Caterpillars are most active at night, often hiding in the soil or in leaf litter near the base of plants during daylight hours. Several moth and butterfly species use violas and their wild relatives as larval food plants, and while this ecological function is valuable in the wider countryside, in a garden display it can quickly reduce ornamental plants to bare stems.

Which Caterpillars Eat Violas and Pansies?

The most common culprits in UK and European gardens include the dark green fritillary and other fritillary butterfly larvae, which use Viola species as their sole larval food plant in the wild. In gardens, various moth larvae — particularly certain noctuids (the large yellowish-green or brown soil-dwelling cutworm caterpillars) — also feed on pansy foliage. Fritillary caterpillars are usually very small and dark when young, becoming larger and more patterned as they mature. Cutworm caterpillars are plump, often curled in a C-shape, and found just below the soil surface or at the base of the plant.

Hand-Picking: Effective and Immediate

Go out with a torch after dark and hand-pick caterpillars from the plants, dropping them into a bucket of soapy water. Check both upper and lower leaf surfaces, the stem base, and the soil immediately around the plants. Repeat on several consecutive evenings until no new feeding damage appears. For small infestations this approach is completely sufficient and avoids any impact on wildlife. If the caterpillars are fritillary larvae, consider whether you can relocate them to a patch of wild violets or a wilder part of the garden rather than destroying them.

Netting to Exclude Egg-Laying Adults

If moth or butterfly adults are laying eggs repeatedly on your plants, fine insect mesh or horticultural fleece draped over a frame above the plants prevents females from reaching the foliage to oviposit. This must be installed early in the season before egg-laying begins. The mesh must be sealed at the edges — lay it on the soil around the planting and weight it down — to prevent adults from finding gaps. This approach is particularly useful for valued container plantings or exhibition plants.

Bacillus thuringiensis (Bt) for Larger Infestations

Bacillus thuringiensis var. kurstaki (Btk) is a naturally occurring soil bacterium that produces proteins toxic to lepidopteran larvae but harmless to mammals, birds, and most beneficial insects. It is available as a spray-on biological insecticide and is approved for organic growing. It must be eaten by the caterpillar to work — spray it directly onto the foliage the caterpillars are eating. It is most effective on young caterpillars in their first few instars and breaks down quickly in sunlight, so reapply every five to seven days while caterpillars are active.

Cutworm-Specific Controls

Cutworm caterpillars that sever plants at soil level are best controlled by forking over the soil around plants to expose larvae to birds and the elements. A biological nematode drench (Steinernema carpocapsae) applied when the soil is warm also parasitises cutworm larvae effectively and is approved for organic use.