Surprisingly, the use of these “accessories” doesn’t spell doom for the organisms being adorned. In fact, it becomes a mutually beneficial alliance. Decorator crabs provide a means for these creatures to travel over vast distances, and the decorations offer protection against predators.

One of the fascinating examples of this phenomenon is the Achaeus spinosus, which cloaks itself in stinging hydrozoa. This mutualistic relationship ensures the crab’s protection against stings while granting the hydrozoa access to a larger feeding area, courtesy of the crab’s mobility.

Decorator crabs attach these marine ornaments to their shells with specialized hooked bristles called setae. In a process reminiscent of Velcro, they choose, pick up, and arrange their selections on these bristles. However, this process is not without its challenges, as decorator crabs can be incredibly selective about their attire. Some crabs sport a modest covering of bristles, while others, like the moss crab, don a full wardrobe of them. The drawback? When they molt to grow further, they shed their carefully selected ornaments and must start afresh.

While many animals use camouflage to hide, decorator crabs have taken this skill to new heights. Their adaptability is astonishing, as a study by zoologist Hugh Bamford Cott discovered that even when moved to a new environment, these crabs immediately begin adjusting their camouflage using locally sourced materials. Their decorative efforts aren’t geared toward attracting mates; rather, they’re a sophisticated survival tactic to shield themselves from predators. With a penchant for adorning themselves with local materials, from seaweeds to bryozoans and hydrozoans, they master the art of invisibility.

Some decorator crabs have raised their fashion game by turning their adornments into defenses. For instance, certain crabs use anemones, urchins, and hydrozoans with stinging capabilities. These accessories deter potential predators by packing a painful punch. Conversely, crabs that apply toxic seaweeds create a distasteful (and potentially lethal) flavor, deterring many natural predators.

However, some decorator crabs go beyond defense and use their “accessories” as weapons. A prime example is the boxer crab, also known as the pom-pom crab, which attaches anemones and arches to its claws, brandishing them when provoked or attacked. The waving of these adorned claws, equipped with stinging cells, is a formidable deterrent. Remarkably, the pom-pom crab’s relationship with sea anemones is vital for the survival of both, as the crab carries the anemone in its claws.

Inventive decorator crab species have even turned their adornments into fishing tools. For instance, they cover their front legs with Hydrichthella epigorgia, a hydrozoan akin to coral. This species consists of tiny polyps that work collectively to capture microscopic food and transfer it to the animal’s mouth. Clever crab species utilize these “fishing rods” to enhance their hunting prowess.

Yet, what do decorator crabs do when their preferred materials, such as sponges, algae, or marine debris, are unavailable? Research by Danielle Dixon and her team at the University of Delaware has shown that these resourceful creatures can adapt to their environment. In an experiment, crabs were offered containers filled with green and red pom-poms resembling Christmas decorations, and surprisingly, they didn’t hesitate to utilize them for a festive touch.

In the enthralling world of decorator crabs, fashion is not just for style; it’s a matter of survival, innovation, and adaptability that continues to astound and inspire.