Caterpillars, the larval stage of butterflies and moths, exist to eat and grow. This period of intense feeding is crucial for their development, allowing them to store the energy and resources needed for their transformation into adult insects. While their appetites are substantial, their diet is often specific, focusing on particular plant species essential for their survival and metamorphosis.
The Host Plant Connection
Caterpillars exhibit a highly selective feeding behavior, largely due to a specialized relationship with “host plants.” These are specific plant species where adult butterflies and moths lay their eggs, ensuring that caterpillars have an immediate and suitable food source. This selectivity stems from a co-evolutionary process, where caterpillars have adapted to tolerate and even utilize certain chemical compounds produced by these plants, some of which might be toxic to other herbivores.
Caterpillars identify their host plants through a combination of chemical cues, such as the unique scent of leaves. These specific plants provide the nutritional balance required for the caterpillar’s rapid growth and development. While a caterpillar might occasionally be found on a non-host plant, it can only feed, digest, and thrive on its designated host, making these plants indispensable for their life cycle.
Common Flowers and Plants Caterpillars Favor
Many familiar flowers and plants serve as host plants for various caterpillar species. For instance, the Monarch butterfly caterpillar feeds exclusively on milkweed (Asclepias species). Without milkweed, Monarch caterpillars cannot survive or complete their metamorphosis.
Garden herbs such as dill, parsley, and fennel, along with other members of the carrot family, are the preferred host plants for Black Swallowtail butterfly caterpillars. These caterpillars consume the foliage, preparing for their transformation into adults. Similarly, Gulf Fritillary butterfly caterpillars feed solely on passionflower vines (Passiflora species), eating the leaves and stems to fuel their development.
Sunflowers (Helianthus annuus) and other plants in the Aster family, including black-eyed Susans, host Checkerspot butterfly caterpillars, such as the Silvery Checkerspot and Gorgone Checkerspot. These caterpillars feed on the leaves. Various species of Fritillary butterflies, including the Great Spangled and Pearl-bordered Fritillaries, depend on violets (Viola species) as their primary food source, with their caterpillars consuming the leaves, flowers, and stems. Common garden plants like clover and other legumes also serve as host plants for caterpillars such as the Clover Looper, Green Cloverworm, and Cloudless Sulphur.
Protecting Your Garden from Caterpillar Damage
While caterpillars are a natural part of the ecosystem and many are beneficial, their voracious appetites can sometimes lead to plant damage in gardens. Identifying the specific type of caterpillar present can help determine if intervention is needed, as some species are considered pests while others are important for local biodiversity. Recognizing signs of their presence, such as chewed leaves, small black droppings (frass), or webbing, can help gardeners assess the situation.
For managing caterpillar populations without harsh chemicals, several organic methods are effective. Hand-picking caterpillars from plants and relocating them or dropping them into a bucket of soapy water is an efficient approach, especially for smaller infestations. Encouraging natural predators like birds, parasitic wasps, and lacewings by planting nectar-rich flowers can help keep caterpillar numbers in check. Physical barriers, such as insect netting or cardboard collars around plant bases, can also deter them. Organic sprays, such as neem oil, work by disrupting feeding and growth or suffocating smaller caterpillars.
Bacillus thuringiensis (Bt), a naturally occurring bacterium, specifically targets and harms only caterpillars after they consume treated leaves, making it safe for other beneficial insects. Observing your garden regularly and understanding the role caterpillars play can help gardeners maintain healthy plants while supporting the broader ecosystem.