Ladybugs, belonging to the beetle family Coccinellidae, are primarily known as beneficial insects. Their diet largely consists of other insects, not plants. While a small subset of the global population consumes plant matter, the vast majority of species found in gardens and fields are voracious predators. This predatory nature makes them highly valued in natural pest control, explaining their presence on plants infested with harmful pests.
The Predatory Diet of the Common Ladybug
The typical ladybug’s diet centers on soft-bodied, slow-moving insects that feed on plants, making them a gardener’s natural ally. Their preferred prey are aphids, often clustered on new plant growth, but their menu is varied. They also consume scale insects, mealybugs, psyllids, whiteflies, and various mites that damage crops and ornamental plants.
This carnivorous appetite is especially pronounced during the larval stage. Ladybug larvae, which look like tiny, dark-colored alligators, are effective hunters that consume large volumes of pests. A single larva can devour approximately 400 medium-sized aphids before it enters the pupal stage.
Adult ladybugs maintain this predatory behavior throughout their lifespan, capable of eating up to 50 aphids per day. Over its life, an adult ladybug can consume thousands of pests, significantly limiting population growth. Some species also supplement their diet with non-prey items like pollen, nectar, and fungal spores when insect prey is scarce.
Why Ladybugs Land on Leaves
When a ladybug is observed on a leaf without visible insects, it is typically engaged in a non-feeding activity related to its life cycle or survival. The most frequent reason for being on foliage is actively hunting for an aphid colony. These beetles use their antennae to detect chemical cues left by pests or honeydew, the sugary excretion produced by aphids, guiding them along the plant.
Another primary reason for landing on leaves is oviposition, the process of laying eggs. Female ladybugs strategically deposit their small, spindle-shaped, yellow-orange eggs in clusters, often on the undersides of leaves near an established pest population. This placement ensures that when the eggs hatch, the young larvae have an immediate and abundant food source.
Leaves also offer protection from the elements and predators, serving as shelter and resting spots. The larva will eventually attach itself to a leaf or stem as it transitions into the immobile pupal stage. During this period, the pupa remains on the plant surface while undergoing metamorphosis before emerging as an adult beetle.
The Exception: Herbivorous Ladybug Species
While the image of the ladybug as a beneficial predator is largely accurate, a small percentage of the Coccinellidae family are phytophagous, meaning they feed exclusively on plants. These herbivorous species can be agricultural pests themselves. The Mexican bean beetle (Epilachna varivestis) is one of the most recognized plant-eating exceptions in North America.
This species targets legumes, such as snap beans, pole beans, and soybeans, consuming the soft tissue of the leaves. Both the adult beetles and their spiny, yellow larvae feed on the foliage, causing a characteristic damage pattern known as “skeletization.” This behavior leaves behind only the network of leaf veins, giving the leaf a lace-like appearance.
Another example is the 28-spotted potato ladybug (Epilachna vigintioctopunctata), a pest of potato, tomato, and squash plants in parts of Asia. These plant-feeding ladybugs often look different from their predatory cousins, sometimes exhibiting a matte finish and a greater number of spots.