The order Coleoptera, commonly known as beetles, constitutes the largest group of animals on Earth, accounting for nearly 400,000 described species. This immense diversity is matched by a vast range of feeding strategies, as beetles are found in virtually every terrestrial and freshwater habitat, consuming nearly every type of organic matter. Their evolutionary success stems in part from their rigid forewings, called elytra, which protect the delicate hindwings and the main body.
This ecological flexibility is enabled by the presence of chewing mouthparts, specifically strong mandibles. These mandibles are adapted for biting and grinding, allowing beetles to process materials ranging from tough wood fibers to fungal hyphae and the exoskeletons of other insects. This structure facilitates a wide spectrum of specialized diets across all life stages, allowing different beetle families to specialize in five major feeding guilds.
Consumers of Living Plant Material
The most common feeding strategy among beetles is phytophagy, the consumption of living plant tissue. This expansive diet includes every part of a plant, from the roots to the flowers. Many insects considered agricultural pests fall into this category.
Some beetles target the photosynthetic machinery of plants. The Japanese beetle, for example, skeletonizes leaves by eating the tissue between the veins. Adult weevils commonly feed on the edges of leaves, leaving behind distinctive notches. This damage reduces the plant’s ability to produce energy.
A different group focuses on feeding below the soil surface, targeting the plant’s energy reserves. Wireworms, the larvae of click beetles (Elateridae), spend years underground consuming live roots, germinating seeds, and tubers. Root weevil larvae cause severe damage by girdling the main roots of shrubs and herbaceous plants.
Other species specialize in consuming woody tissue, boring into the vascular systems of living trees. The larvae of long-horned beetles (Cerambycidae) and metallic wood-boring beetles (Buprestidae), such as the emerald ash borer, tunnel through the phloem and cambium. By feeding on this layer beneath the bark, these larvae sever the tree’s ability to transport water and sugars, leading to the tree’s death.
Flower and pollen feeders represent another type of plant consumption, often playing a role in pollination. Flower beetles (Cetoniinae) are often seen on blossoms, where they consume nectar, pollen, and soft petal tissues. They are also attracted to sugary plant exudates and the fermenting juices of ripe or damaged fruits.
The Role of Predatory Beetles
A significant portion of the beetle population are carnivores that hunt and consume other invertebrates. This predatory lifestyle is prevalent in the families Carabidae (ground beetles), Coccinellidae (lady beetles), and Staphylinidae (rove beetles). These hunters help regulate populations of other insects.
Lady beetles are the most recognized predatory group, specializing in soft-bodied prey like aphids and scale insects. Both the adults and larvae actively search for and consume these small pests. A single lady beetle can consume thousands of aphids over its lifetime, making them effective agents in agricultural and garden ecosystems.
Ground beetles are primarily nocturnal predators that use their powerful mandibles to subdue prey found on the soil surface. They consume a wide variety of invertebrates, including slugs, snails, caterpillars, and the eggs and larvae of other insects. Many ground beetle larvae also hunt root maggots and other subterranean pests in the soil.
Tiger beetles (Cicindelinae), known for their speed, employ a “pause-and-pursue” hunting strategy to capture small insects and arthropods. They sprint rapidly toward their prey, stop to regain focus with their sharp vision, and then strike with large mandibles. Rove beetles are generalist predators whose larvae and adults hunt for small prey in leaf litter, under bark, and near decaying matter, consuming organisms like fly maggots and springtails.
Recyclers of Dead Organic Matter
Many beetles fulfill the role of detritivores, consuming non-living organic matter to cycle nutrients back into the soil. This scavenging behavior, known as saprophagy, breaks down complex materials from both plant and animal origins.
A specialized group of carrion feeders, such as burying beetles (Silphidae), locate and process small animal carcasses. The adult beetles work in pairs to bury the remains, strip the fur, and form the meat into a protective ball for their eggs. This process removes carcasses from the environment and provides a sheltered food source for their developing larvae.
Dung beetles (Scarabaeidae) consume animal feces, a diet important for ecosystem health. These beetles quickly bury or roll away dung, reducing habitat for nuisance fly breeding and preventing parasite growth. By burying the dung, they aerate the soil and accelerate the return of nutrients, like nitrogen, to the plant life cycle.
Other decomposers focus on dead plant material, particularly wood and leaf litter. The larvae of stag beetles (Lucanidae) spend years burrowing through and consuming decaying, soft wood, which is rich in microorganisms. Darkling beetles (Tenebrionidae) and chafer grubs feed on decomposing vegetable matter found in forest leaf litter and topsoil. These feeders initiate the breakdown of tough cellulose, making its stored energy available to the wider ecosystem.
Highly Specialized and Mycophagous Feeders
While most beetles fall into the major feeding categories, some lineages have developed highly specialized diets. Among these are the mycophagous beetles, which specialize in eating fungi, molds, and spores. This diet is common across several unrelated beetle families, including pleasing fungus beetles (Endomychidae) and some lady beetles.
Some lady beetles, for example, primarily consume the spores and mycelium of powdery mildews, rather than insects. Specialized fungus-farming beetles, known as ambrosia beetles, bore tunnels into wood where they introduce and cultivate specific fungi. The larvae then consume this fungal growth, or “ambrosia,” which is easier to digest than the wood itself.
Other specialized feeders have adapted to concentrated food sources. Carpet beetles (Dermestidae) are scavengers that focus on dried animal products, consuming:
- Wool
- Silk
- Feathers
- Dried museum specimens
Similarly, stored product pests, such as flour beetles, thrive on dried grains and milled products, making them common inhabitants of seed caches and domestic pantries.