Lots of us will be familiar with organisms like decorator crabs that utilize bits and pieces of their environment, especially living sea anemones, as a form of camouflage and protection. Examples of terrestrial insects attaching bits and pieces of lichens to their body are not unheard of either. However, there are at least two groups of arthropods that take their camouflage to a whole new level by actively growing miniature gardens on their bodies.
Little is known about these garden-growing arthropods. To date, these miniature gardens have only been reported on a few species of weevil in the genus Gymnopholus as well as a species of millipede called Psammodesmus bryophorus. Coined epizoic symbiosis, it is thought that these gardens serve as a form of protection by camouflaging the gardeners against the backdrop of their environment.
Indeed, both groups of arthropods frequent exposed areas. What is most remarkable about this relationship is that these plants were not placed on the carapace from elsewhere in the environment. Instead, they have been actively growing there from the beginning. Closer inspection of the cuticle of these arthropods reveals unique structural adaptations like pits and hairs that provide favorable microclimates for spores to germinate and grow.
The plant communities largely consist of mosses and liverworts. At least 5 different liverwort families are represented and at least one family of moss. Even more remarkable is the fact that even these small botanical communities are enough to support a miniature ecosystem of their own. Researchers have found numerous algae such as diatoms, lichens, and a variety of fungi growing amidst the mosses and liverworts. These in turn support small communities of mites. It appears that an entire unknown ecosystem lives on the backs of these mysterious arthropods.
There is still much to be learned about this symbiotic relationship. Although camouflage is the leading hypothesis, no work has been done to actually investigate the benefits these arthropods receive from actively growing these miniature gardens on their backs. Mysteries still abound. For instance, in the case of the millipede, gardens are found more frequently on the backs of males than on the backs of females. Could it be that males spend more time searching their environment and thus benefit from the added camouflage? Only further research will tell.