The praying mantis is recognized for its unique posture and ability to blend seamlessly into its surroundings. This camouflage makes its coloration a primary feature of its biology. Many people observe that a green mantis eventually turns brown after death, prompting the question of whether this is a natural biological process or simply decomposition. The answer involves the insect’s pigments and the physical effects of its environment after life has ceased.
The Immediate Answer
A praying mantis, especially a green one, will almost always turn a deeper shade of brown or black after death. This color change is not a biological response to dying, but the result of physical and chemical processes that occur when the insect’s regulatory systems shut down. The shift is primarily driven by the loss of water from the body and the subsequent breakdown of fragile organic compounds. This browning effect is a clear sign of post-mortem changes, moving the mantis to a desiccated state. In a dry environment, the body loses moisture quickly, which alters the light-reflecting properties of the exterior shell and combines with chemical oxidation to produce the darker coloration.
Understanding Living Praying Mantis Coloration
While alive, a praying mantis’s color is a sophisticated adaptation determined by genetics and environmental factors. Mantises are typically green, brown, or a mixture of both, depending on the need for camouflage in their habitat. Coloration is achieved through pigments like carotenoids and tetrapyrroles, which are embedded within the insect’s outer layers and acquired through the mantis’s diet. The ability to change color is a slow, morphological process, occurring only when the mantis molts and sheds its exoskeleton. This chromatic adaptation is a long-term survival strategy influenced by external factors like temperature, humidity, and the background color.
Desiccation and Post-Mortem Pigment Changes
The noticeable post-mortem browning is a direct consequence of the body’s inability to maintain cellular integrity and hydration. The first mechanism at play is desiccation, which is the extreme drying out of the body tissues and the exoskeleton, or cuticle. As the internal water content evaporates, the remaining tissue shrinks, and the structure of the cuticle changes, leading to a darker appearance due to altered light scattering properties. This loss of moisture also concentrates the remaining pigments, contributing to the perceived darkening.
Chemical changes are also significant, particularly for green mantises. The green coloration is often due to pigments that are highly susceptible to chemical degradation, such as chlorophyll-like tetrapyrrole compounds. Once the mantis dies, the regulatory processes that stabilize these pigments cease, allowing them to rapidly oxidize upon exposure to air. This oxidation process breaks down the delicate green compounds, often leaving behind more stable, darker pigments, such as melanins or residual brown chitin.
The internal fluids and soft tissues also undergo decomposition that contributes to the darkening. The breakdown of organic material by enzymes and bacteria releases substances that stain the surrounding tissue brown or black. In the mantis, the combination of pigment oxidation and rapid desiccation makes the shift to a dark brown or black hue a very rapid and pronounced phenomenon.