Decorator crabs are a fascinating group of crustaceans that belong to the superfamily Majoidea. They have earned their name due to their remarkable ability to use materials from their environment for camouflage or to ward off predators. These remarkable creatures, which include spider crabs, sea crabs, moss crabs, toothed crabs, and arrow crabs, encompass over 700 different species within the superfamily Majoidea, known as ornamental crabs. These crabs often employ creative camouflage techniques, adorning their bodies with a diverse array of “ornaments” that often exceed our imagination.
Ornamental crabs, which belong to several different species within the superfamily Majoidea, master the art of blending in and repelling potential threats through their innovative use of environmental materials. They decorate themselves by affixing primarily sedentary animals and plants, such as corals, seaweeds, sponges, sea fans, anemones, seagrasses, sea urchins, bryozoans, hydrozoans, and even other small crustaceans to their bodies. This inventive camouflage technique was meticulously observed and documented by William Bateson in 1889, who noted that these crabs could recreate their camouflage cover if it was deliberately removed, duplicating it precisely.
Remarkably, using other creatures as camouflage does not entail harm; it’s a symbiotic and mutually beneficial relationship. In the natural world, animals often adapt to blend in with their surroundings, enabling prey to evade predators and predators to stalk their prey undetected.
The specialization of ornamental crabs in their selection of camouflage materials is evident from research conducted in 1940 by British zoologist and camouflage expert Hugh Bamford Cott. His study of the great spider crab (Hyas araneus) in the Atlantic Ocean showed the incredible diversity in their choice of camouflage. Some species use specific materials for camouflage, like the pelia tumida, which decorates itself exclusively with sponges. Others, like MacroPodia rostrata and Libinia dubia, select toxic algae Dictyotaheesiain in certain regions, while Inachus phalangium picks similar algae for the most exposed body parts. Additionally, Stenocionops furcata opts for three colors of Calliactis anemone for its shell.
Cott further demonstrated that these decorative crabs adapt their camouflage to their environment when relocated. They use local materials to rebuild their camouflage, making each crab’s appearance unique to its surroundings. These ornamental crabs are found in oceans and seas around the world. They are visible at night due to the reflection of their eyes in the water, but their camouflage is so effective that they are difficult to spot during the day.
In addition to using camouflage for protection, some crab species have gone a step further by using ornaments to bolster their defenses. For instance, they may attach sea anemones, sea urchins, and hydrozoans, all of which can deliver a painful sting to potential predators that venture too close. On the flip side, adorning themselves with poisonous seaweeds can leave a disagreeable (and potentially fatal) taste in the mouths of would-be attackers.
The lifespan of these crabs remains undetermined. Some species even use their camouflage for offense, like the boxer crab (Lybia tessellata), which attaches sea anemones and sea urchins to its claws and wields them as weapons. With approximately 700 species of ornamental crabs, including Acanthonyx dentatus, MacroPodia rostrata, Oregonia gracilis, Libinia emarginata, Achaeus spinosus, and Camposcia retusa, the total population size is unknown.
When provoked or attacked by predators, these crabs intimidate their foes by waving sea anemones with tentacles equipped with cnidocytes (stinging cells). Some ornamental crabs even exploit aquatic species like Hydrichthella epigorgia, which resembles corals and is composed of numerous small polyps working together as a collective organism. In a cunning twist, certain species have attached these sticky polyps to their claws to create effective makeshift fishing rods.
