June bugs, also known as May beetles or chafers, are common nocturnal insects that emerge in late spring and early summer. These beetles are often encountered fluttering around outdoor lights during warmer evenings.
Measuring a June Bug
Adult June bugs measure between 1/2 inch and 1 inch (12 to 25 millimeters) in length. This size places them among larger common beetles, often comparable to a human thumbnail or small coin. Their width and height are proportionate to their length, contributing to their thick, oval, and rounded body shape.
Variations exist among June bug species. For instance, the Green June Beetle (Cotinis nitida) measures around 1 inch, while the Ten-lined June Beetle (Polyphylla decemlineata) can reach up to 1.5 inches (3 centimeters). The larval stage, known as a white grub, can be larger than the adult, ranging from 3/4 inch to 2 inches (25 to 50 millimeters) in length.
Identifying a June Bug by Appearance
June bugs have distinct visual characteristics. Most common species are reddish-brown to dark brown or nearly black, giving them a uniform appearance. Some species, like the Green June Beetle, exhibit a striking metallic green coloration.
These beetles have a robust, oval body encased in a hard exoskeleton, which often appears glossy or iridescent, especially on their elytra (wing covers). They have six sturdy, jointed legs adapted for movement and burrowing. Their antennae are clubbed, and in some species, they can be fanned open or feature large, distinctive plates, especially in males.
Why June Bugs Vary in Size
June bug size varies primarily due to the many species within the “June bug” designation. The genus Phyllophaga, which includes many commonly called June bugs, has over 800 known species in North America alone, and each species has a different average size. For example, the common June beetle (Phyllophaga species) can range from 12 to 35 millimeters, while the Green June beetle measures 15 to 22 millimeters.
Environmental factors also play a role in individual size. Food availability during their prolonged larval stage impacts their growth and adult size. June bug larvae, or grubs, spend one to four years developing underground. The quality and abundance of their food source during this period contribute to their final adult dimensions.
How Size Impacts June Bug Behavior
The large, heavy bodies of June bugs, combined with their disproportionate wings, result in a clumsy, erratic flight pattern. Their flight produces a distinct buzzing sound, and they collide with objects like windows and walls. After landing, they may struggle to right themselves if they end up on their backs.
Their physical dimensions also influence their feeding habits. Adult June bugs consume the leaves of trees and shrubs, including oak, walnut, maple, and certain fruit trees. Conversely, their large larvae, the white grubs, feed on the roots of grasses and other plants underground, which can damage lawns and agricultural fields. Their size also makes them a calorie-rich food source for predators, including birds, small mammals (skunks, moles), and other insects.