The praying mantis is a predatory insect known for its specialized forelimbs, which it holds in a posture that suggests prayer, and its remarkable ability to blend into its surroundings. Many species display a striking color-shifting ability, moving between a bright green and a dull brown throughout their life cycle. This shift is a complex physiological process that allows the mantis to perfectly match the color of its habitat. The transition from green to brown is a direct adaptation to seasonal changes, ensuring the insect maintains its camouflage as its environment dries out.
The Biological Mechanism of Color Change
The process of color change in a mantis is a morphological adaptation, meaning it involves the physical alteration or relocation of pigments within the insect’s outer layer, or integument. Unlike the near-instantaneous changes seen in chameleons, the mantis’s color shift is a slow process that typically occurs only when the insect sheds its exoskeleton, a process known as molting. This means the mantis is locked into its current color until it undergoes the next molt.
The mantis’s two primary color components rely on different pigment groups stored beneath the rigid exoskeleton. Green coloration is often achieved through a combination of a yellow carotenoid pigment and a blue-green tetrapyrrole pigment. Brown coloration, however, is a result of the synthesis and accumulation of pigments like ommochromes, which are derived from amino acids. When the environmental signal for a brown body is received, the production of green-associated pigments is suppressed, and the brown ommochromes become the dominant color.
Environmental Triggers for Turning Brown
The decision to develop a brown body color is directly driven by the visual information the mantis receives from its immediate surroundings, a phenomenon called background matching. Studies have shown that mantis nymphs raised in enclosures lined with brown paper or sticks will molt into a brown form, while those on green foliage become green. This suggests that the insect’s nervous system registers the dominant color of its substrate and initiates the necessary physiological response.
The shift to brown is also closely associated with environmental conditions that cause vegetation to dry out, such as high temperatures and low humidity. In the late summer and autumn, as green leaves wither and turn into brown, dry litter, the mantis must adapt to survive. The visual cue of dry, brown vegetation triggers a hormonal signal, which then programs the pigment synthesis pathways for the upcoming molt. This ensures that the newly hardened exoskeleton of the next life stage is the appropriate brown color for the new, drier habitat.
Camouflage and Survival Advantage
The ability of a mantis to turn brown serves the fundamental evolutionary purpose of camouflage, which provides a dual advantage in the wild. A brown mantis perfectly positioned on bark, a dead branch, or dried grasses becomes nearly invisible to avian predators that hunt by sight. This defensive camouflage vastly increases the mantis’s chances of reaching adulthood and reproducing.
The same brown coloration is also a powerful offensive tool, making the mantis a highly effective ambush hunter. By blending seamlessly with the brown background of a forest floor or a dried thicket, the mantis can wait motionless for unsuspecting prey, such as flies or grasshoppers, to wander into striking range. This strategy, known as sit-and-wait predation, is significantly enhanced by the ability to match the surrounding environment.