The June Bug, which generally refers to various scarab beetles like the genus Phyllophaga or the Green June Beetle (Cotinis nitida), possesses hair-like structures. These projections give the insects a fuzzy or bristly appearance, particularly noticeable on the underside of their bodies and legs. While they resemble mammalian hair, these structures are fundamentally different in biological composition and origin. They are specialized extensions of the insect’s exoskeleton that serve several important biological roles.
Setae: The Anatomy of Insect “Hair”
The hair-like structures on a June Bug are scientifically termed setae, which are microscopic extensions of the insect’s cuticle or hard outer layer. Setae are primarily composed of chitin, a tough, nitrogen-containing polysaccharide, making them chemically distinct from mammalian hair, which is made of the protein keratin. Unlike hair that grows from a follicle, setae are formed by specialized epidermal cells that create an outgrowth of the exoskeleton.
The appearance of setae varies significantly depending on their location and function on the beetle’s body. On the thorax and abdomen, they may appear as a dense, velvety fuzz, while on the legs they are often stiff, robust bristles. Each seta is a non-living, hollow tube that articulates at the base, allowing it to move freely. This articulation is often linked directly to a sensory neuron, transforming the physical movement of the seta into a nerve signal.
Essential Functions of the Setae
One significant function of setae is mechanoreception, where they act as tiny sensory antennae, detecting movement in the air or on surfaces. A sensory neuron at the base of each seta registers its deflection, allowing the beetle to perceive air currents, vibrations, and tactile cues crucial for navigation and predator avoidance. Setae also play a substantial role in locomotion. Specialized adhesive setae on the tarsi (feet) help the adult beetle gain purchase, aiding in climbing on smooth surfaces.
The larvae of the Green June Beetle (Cotinis nitida) possess stiff, ambulatory bristles on their abdomen that are essential for their unique method of movement, allowing them to crawl efficiently on their backs through the soil. Setae also provide a layer of protection and insulation. They help repel water, keeping the spiracles (the insect’s breathing pores) clear of moisture and debris. In some species, the density of the setae acts as a physical barrier, protecting the softer cuticle from abrasion as the beetle burrows.
Regional Names and Identification
The term “June Bug” is a common name applied regionally to several different species of scarab beetles, including the brown Phyllophaga genus and the metallic green Cotinis nitida. All these beetles possess setae, and the appearance of this “hair” can be a distinguishing feature. Phyllophaga species are generally brown or reddish-brown and often have dense, fine setae on their underside, contributing to a fuzzy appearance. The Green June Beetle (Cotinis nitida) is distinctively metallic green, but its larvae are noted for their stiff abdominal bristles, which aid in identification during the grub stage.