The order Coleoptera, commonly known as beetles, represents the most diverse group of insects, encompassing hundreds of thousands of species globally. The term “brown beetle” is a general description that applies to countless types of these insects, whose diets are as varied as their forms. Determining what a brown beetle eats depends entirely on its specific species and its current stage of life. These creatures can range from voracious plant-eaters found outdoors to destructive scavengers consuming stored goods inside homes.
The Necessary Distinction: Identifying Common Brown Beetles
The sheer number of beetle species means that identifying the family is the only way to understand its diet. Many common brown beetles belong to the Scarabidae family, including June bugs and the Japanese beetle. These robust, convex-shaped insects primarily feed on living plant matter as adults. Other prevalent types are the weevils, characterized by their elongated snouts, which are pests of live plants or stored grains. The Dermestidae family, such as the varied carpet beetle, specializes in consuming dried animal and plant material, making them household nuisances.
Outdoor Diets: Consumers of Roots, Foliage, and Sap
Brown beetles found in gardens and natural environments are almost exclusively herbivores, specializing in consuming various parts of living plants. Adult June bugs are nocturnal feeders that consume the leaves of many deciduous trees, including oak, maple, and hickory. This foliage consumption generally causes ragged edges on leaves but rarely threatens the plant’s survival. In contrast, the Japanese beetle is a more aggressive feeder, consuming over 300 different plant species by skeletonizing the leaves.
Many weevil species, recognizable by their distinct rostrum or snout, focus their diet on specific plant parts. The adult plum curculio targets fruit and fruit-bearing trees, often damaging apples, plums, and peaches. Root weevils, like the strawberry root weevil, feed on the roots of various plants, including strawberries and evergreen shrubs.
Some beetles also engage in secondary consumption, feeding on plant sap or decaying organic matter rather than living tissue. This behavior is crucial for nutrient cycling in the ecosystem, often involving fermenting fruit or tree sap that attracts them in large numbers.
Indoor Diets: Pests of Stored Products and Natural Fibers
Brown beetles that inhabit human structures primarily feed on processed organic materials and dried goods. One major group is the stored product pests, including the confused and red flour beetles, which are common pantry invaders. These beetles thrive on milled grain products like flour, cereal, cake mix, and pet foods, often infesting improperly sealed items. Grain weevils, such as the granary and rice weevil, target whole, intact grains like rice and wheat kernels, sometimes feeding on pasta and other hard starches.
Another distinct category of indoor pests is the natural fiber and debris feeders, exemplified by the carpet beetle. The larvae of this family focus on keratin, a protein found in animal-based materials. They cause damage to clothing, upholstery, and carpets by consuming materials such as:
- Wool
- Silk
- Feathers
- Leather
- Fur
- Dried animal specimens
These beetles also scavenge on organic debris, including lint, pet hair, and dried insect carcasses in dark, undisturbed areas.
The Larval Stage: Different Bodies, Different Menus
The life cycle of a brown beetle involves a complete metamorphosis, and the larval stage often features a dramatically different diet than the adult. For many species, the larvae, commonly called grubs, are the most destructive feeders. Adult carpet beetles fly outdoors to consume pollen and nectar. However, their larvae remain indoors, feeding for months or years on natural fibers to accumulate the necessary protein and nutrients for pupation.
A similar dietary shift occurs in outdoor species like the June bug. While adults consume the leaves of trees and shrubs, the C-shaped larvae, or white grubs, spend their time underground eating the roots of grasses and other plants. This root-feeding behavior causes significant damage to lawns and turf, often resulting in large, dead patches of grass. The larval stage is fundamentally a period of intensive nutrient storage, explaining the difference in the type of food consumed compared to the adult.