What Do Beetles Eat?
Beetles (order Coleoptera) are the most species-rich order of insects, with over 400,000 described species — roughly 25% of all known animal species. As the famous biologist J.B.S. Haldane reportedly quipped, the Creator has "an inordinate fondness for beetles." This extraordinary diversity is mirrored in their diets: beetles exploit virtually every organic food source on Earth.
Dietary Categories
Beetle diets can be broadly classified into several feeding guilds, though many species are omnivorous or shift diets between larval and adult stages.
| Feeding Type | Description | Example Families |
|---|---|---|
| Herbivorous | Feeding on living plant tissue — leaves, roots, flowers, seeds, or sap | Chrysomelidae (leaf beetles), Curculionidae (weevils) |
| Predatory | Hunting and consuming other invertebrates | Carabidae (ground beetles), Coccinellidae (ladybirds) |
| Xylophagous | Feeding on wood, often aided by symbiotic fungi or gut microbes | Cerambycidae (longhorn beetles), Scolytinae (bark beetles) |
| Saprophagous | Feeding on decaying organic matter — dead plants, carrion, dung | Silphidae (carrion beetles), Scarabaeidae (dung beetles) |
| Mycophagous | Feeding on fungi, including mushrooms and moulds | Erotylidae (pleasing fungus beetles), Ciidae |
| Detritivorous | Consuming fine particulate organic matter and leaf litter | Ptinidae (spider beetles), some Tenebrionidae |
Herbivorous Beetles
The majority of beetle species are herbivores. Leaf beetles (Chrysomelidae), with over 35,000 species, are among the most familiar. The Colorado potato beetle (Leptinotarsa decemlineata) is a notorious crop pest, while the lily beetle (Lilioceris lilii) is a striking red species that devastates ornamental lilies in British gardens.
Weevils (Curculionidae), with more than 60,000 species, are the largest beetle family. Their elongated snouts are used for boring into plant tissue to feed and lay eggs. Many are significant agricultural pests, including the grain weevil (Sitophilus granarius) and the boll weevil (Anthonomus grandis).
Herbivore Specialists
- Many herbivorous beetles are monophagous — feeding on only one plant species or genus.
- The tansy beetle (Chrysolina graminis), one of the UK's rarest insects, feeds almost exclusively on tansy (Tanacetum vulgare).
- Co-evolution between beetles and plants has driven the diversification of both groups over millions of years.
Predatory Beetles
Ground beetles (Carabidae) are among the most important insect predators in temperate ecosystems. Species such as the violet ground beetle (Carabus violaceus) hunt slugs, snails, and other invertebrates at night. Ladybirds (Coccinellidae) are beloved by gardeners for consuming vast numbers of aphids — a single seven-spot ladybird (Coccinella septempunctata) may eat over 5,000 aphids during its lifetime.
Tiger beetles (Cicindelinae) are among the fastest running insects relative to their body size, pursuing prey on open ground with remarkable speed and agility. Their large eyes and powerful mandibles make them effective ambush and pursuit predators.
Did you know? The great diving beetle (Dytiscus marginalis) is a voracious aquatic predator. Both adults and larvae hunt tadpoles, small fish, and other invertebrates. The larvae are nicknamed "water tigers" for their aggressive hunting behaviour and powerful, sickle-shaped mandibles.
Wood-Feeding Beetles
Numerous beetle families specialise in eating wood (xylophagy). Longhorn beetles (Cerambycidae) have larvae that bore through timber for months or even years. The house longhorn beetle (Hylotrupes bajulus) is a destructive pest of structural timber. Bark beetles (Scolytinae) live beneath the bark of trees, feeding on the nutritious phloem layer and often introducing pathogenic fungi.
Dung Beetles and Decomposers
Dung beetles (Scarabaeinae) perform an invaluable ecosystem service by burying and consuming animal dung. In doing so, they recycle nutrients, aerate soil, reduce parasite loads, and even limit greenhouse gas emissions from livestock dung. The ancient Egyptians revered the scarab beetle (Scarabaeus sacer) as a symbol of rebirth and the god Khepri.
Larval vs. Adult Diets
In many beetle species, the larva and adult have completely different diets. Stag beetle (Lucanus cervus) larvae feed on decaying wood for up to seven years, while the adults barely feed at all, occasionally lapping tree sap. Conversely, ladybird larvae and adults both feed on aphids, making them doubly useful in gardens.
Key Takeaway
The extraordinary dietary diversity of beetles — spanning herbivory, predation, wood-boring, dung-feeding, fungus-eating, and scavenging — is a key factor in their evolutionary success. This dietary flexibility has allowed beetles to colonise virtually every terrestrial and freshwater habitat on Earth, making them the most species-rich order of animals.