Some spiders possess the remarkable ability to change their body coloration. Not all spiders can change color, but certain types, particularly ambush predators, exhibit this trait. This allows them to alter their appearance, often to blend in with their surroundings or for survival.
Mechanisms of Color Change
Spiders change color through two main biological processes: physiological and morphological. Physiological color change involves rapid adjustments, typically within minutes to hours. This occurs by altering the distribution or concentration of existing pigments or light-reflecting structures within specialized cells. This rapid change is often due to the movement of guanine crystals, which are responsible for white coloration and can be retracted or expanded to reveal or obscure underlying pigments. For instance, some orb-web spiders can expand their guanocytes to appear white.
Morphological color change is a slower process, taking days or even weeks. This type of change involves the actual synthesis or degradation of pigments, requiring more time. For example, crab spiders, such as Misumena vatia, produce yellow pigments called ommochromes when on yellow flowers and withdraw them when on white flowers. The transformation from white to yellow can take between 10 to 25 days, while changing back from yellow to white is typically faster (about 6 days). This process involves complex biochemical pathways, where compounds like 3-hydroxy-kynurenine and xanthommatin contribute to yellow pigmentation.
Purposes of Color Change
Color change provides spiders with adaptive advantages, primarily aiding in survival and reproduction. A prominent purpose is camouflage, allowing spiders to blend seamlessly with their environment to evade predators or ambush prey. For example, crab spiders often match the color of the flowers they inhabit, making them nearly invisible to pollinators they hunt and to birds that might prey on them.
Mimicry is another purpose, where spiders use color change to imitate other animals or elements of their surroundings. Some spiders might resemble bird droppings, using this disguise to attract flies while deterring predators. Color change might also play a role in communication, potentially signaling to mates or rivals, although this aspect is not as widely studied in spiders.
Notable Color-Changing Spiders
Several spider species are recognized for their ability to change color. The goldenrod crab spider (Misumena vatia) is a well-known example. Females of this species can change between white and yellow to match the flowers where they lie in wait for prey. This transformation is not instantaneous, often taking several days, but it aids their ambush hunting strategy.
Another species, Thomisus onustus, a European crab spider, can shift between white, yellow, and pink to blend with flowers it occupies. The green huntsman spider (Micrommata virescens) exhibits seasonal color change, maintaining a vibrant green in spring and summer, then shifting to a pale yellow or brown as autumn approaches, adapting to changing foliage. While individual spiny orb-weavers (Gasteracantha cancriformis) do not rapidly change color, their populations can exhibit shifts in predominant coloration based on seasonal and habitat conditions.