Many people imagine cockroaches as uniformly brown insects, but some common pest species are defined by distinct markings. These color patterns are not random; they serve as a primary means of identification between different species, especially those that infest human structures. The presence or absence of stripes, and their specific location, provides a quick visual clue about the type of cockroach encountered.
Identifying Cockroach Species With Stripes
The clearest example of a striped cockroach is the German cockroach (Blattella germanica), one of the most widespread household pests globally. Adults are small, light tan or brownish yellow insects, measuring about one-half to five-eighths of an inch long. They are easily recognizable by the two dark, parallel streaks running lengthwise on the pronotum, the shield-like segment immediately behind the head. These markings are often described as “racing stripes” and are present on both the adult and nymph stages.
The Asian cockroach (Blattella asahinai) also possesses these same two dark parallel stripes behind the head. Due to their nearly identical appearance, the Asian cockroach is often confused with the German cockroach. However, the Asian species is a proficient flyer and strongly attracted to light, unlike its indoor-dwelling relative. The presence of these parallel stripes on the pronotum is a defining feature of the Blattella genus.
Common Cockroach Species Without Distinct Stripes
Many common pest species lack the prominent parallel pronotal stripes seen on the German cockroach. The American cockroach (Periplaneta americana), which is much larger, features a uniform reddish-brown body. It has a marking on its pronotum that presents as a pale yellow band around the margin, contrasting with the central reddish-brown shield, rather than two distinct dark stripes.
The Oriental cockroach (Blatta orientalis) has a glossy, uniform dark brown or black coloration. This species has no stripes or prominent bands and is often referred to as a “black beetle cockroach.” The brown-banded cockroach (Supella longipalpa) has a name that suggests stripes, but its markings differ from the German cockroach. Instead of pronotal stripes, this species has two light yellow or tan bands that run transversely across the body and wings. These transverse bands are distinct from the German cockroach’s longitudinal parallel stripes, aiding in identification.
The Purpose of Cockroach Coloration
Cockroach coloration, whether striped or uniform, plays a functional role in survival and behavior. The dark pigmentation in the insect cuticle is primarily due to melanin, a compound involved in the hardening of the exoskeleton, a process called sclerotization. Darker areas of the cuticle, such as the German cockroach’s stripes, are often sites of increased structural reinforcement.
Pigmentation aids in protection from the environment, including defense against water loss and UV radiation. The overall color pattern often serves as camouflage, allowing the insect to blend into its preferred habitat. For example, the uniform dark color of the Oriental cockroach helps it disappear in the damp, dark environments it favors. Coloration also relates to social communication, impacting male courtship behavior and female pheromone response in the German cockroach.