June beetles, commonly referred to as “June bugs,” are scarab beetles belonging primarily to the genus Phyllophaga and related genera like Cotinis. These insects are a ubiquitous component of California’s ecosystems, engaging in complex interactions with both natural and managed environments. Their presence highlights a dual ecological function: they act as engineers of soil health while simultaneously posing challenges to agricultural and ornamental plantings. This exploration details how these common insects integrate into the state’s natural history and agricultural landscape.
Identification and Life Cycle in California
The June beetles found across California vary in appearance, with common species including the reddish-brown Common June Beetle (Phyllophaga) and the metallic green Figeater Beetle (Cotinis mutabilis). Adult beetles are robust, oval-shaped insects ranging from a half-inch to over an inch in length, often appearing in late spring or early summer evenings. They are sometimes mistaken for the smaller, invasive Japanese beetle, which is not widely established in California.
The immature stage, known as a white grub, is the life stage most consequential to the ecosystem. Grubs are characterized by a cream-colored, C-shaped body with a distinct brown head capsule. The life cycle can span one to two years, depending on the species and local climate. For example, the Figeater Beetle typically completes its cycle in a single year, while the Tenlined June Beetle (Polyphylla decemlineata) requires two years. Grubs spend the majority of their developmental time buried in the soil, overwintering before emerging as adults to mate during the warmer months.
Contributions to Soil Health and Nutrient Cycling
The prolonged period June beetle grubs spend beneath the surface makes them significant contributors to soil ecology. Grubs of some species, like the Figeater Beetle, primarily consume decaying organic matter, such as compost, mulch, and lawn thatch. This feeding process facilitates the physical breakdown of plant debris and accelerates its conversion back into usable soil components. By ingesting this material, the grubs help release trapped nutrients, including nitrogen, phosphorus, and potassium, making them available for plant uptake.
Their constant movement through the soil profile also provides a mechanical benefit. As the grubs tunnel, they create channels that physically aerate the soil, improving water infiltration and gas exchange necessary for healthy root growth. This physical mixing action also redistributes organic matter and microorganisms throughout the soil layers. The cumulative effect of the grubs’ feeding and burrowing improves overall soil structure and fertility, supporting the health of the broader plant community.
Position in the California Food Web
June beetles, in both larval and adult forms, represent a substantial energy source for a variety of California wildlife. The grubs are a favored food item for several small mammals that actively dig through the soil to locate them. Raccoons, skunks, and moles frequently forage in lawns and garden beds, leaving behind signs of their search for the subterranean larvae. This feeding behavior demonstrates the grubs’ role in transferring energy from the soil environment to higher trophic levels.
Above ground, the adult beetles are an important seasonal food source for various bird species, including American crows and robins, especially during their peak emergence. Bats, being nocturnal hunters, also consume the flying adults as they are attracted to lights at night. Specialized insect predators further integrate the June beetle into the food web, such as parasitic scoliid wasps. These wasps paralyze the grubs and lay an egg on them, using the larvae as a living incubator for their young.
Ecological Impact as Horticultural Pests
The natural actions of June beetles put them in direct conflict with human interests, establishing them as significant horticultural pests in California’s managed landscapes. The damage is split between the larval and adult stages, targeting different parts of cultivated plants. Grubs of certain species, notably those in the Phyllophaga genus and the Tenlined June Beetle, primarily feed on the fibrous roots of turfgrass, ornamentals, and agricultural crops. This root pruning activity can cause sections of lawn to turn brown and die, often feeling spongy underfoot due to severed roots.
In agricultural settings, particularly orchards, root feeding by grubs can severely injure or even kill young trees. The adults also contribute to plant damage by feeding on foliage, a habit noticeable on fruit trees like avocado and stone fruits, or on grapevines. This conflict is often exacerbated by modern practices like irrigation, which creates the moist, organically rich soil conditions ideal for egg-laying and grub development. The beetle’s natural life cycle, while beneficial in a wild ecosystem, becomes detrimental when interacting with high-value managed crops and manicured landscapes.