And I bet you thought dragons didn’t exist. Glaucus atlanticus, more commonly called the “blue dragon,” the “blue angel,” the “sea swallow,” or the “blue sea slug,” is an unusual mollusk devoid of a shell. The brilliant blue and silver markings provide contrasting camouflage for the creature through counter-shading, allowing the Blue Dragon to be camouflaged both above and below. The vivid colors also warn of its extremely venomous nature. Common for slugs, the Blue Dragon has a singular muscular foot and rhinopores that provide sensation. It spends most of its life floating upside-down on the surface of the water due to a gas-filled sac in its stomach. These tiny nudibranchs can have up to three sets of long, black cerata (appendages on either side of its body) which can be utilized for respiration, digestion, and protection from predators by storing venom. Typically only an inch long in length, the miniature creature has never been documented to grow more than 1.2 inches and is usually very slim and sleek. They reproduce as hermaphrodites, as they all have both female and male reproductive parts, and both mating partners will produce egg strings. These eggs are typically laid on drift wood or the carcasses of their parents’ kills where they grow and develop air sacs of their own. The Blue Dragon is in no danger of extinction as the population thrives in every location. Accustomed to tropical, warm waters, the Blue Dragon can be found along the coasts of South Africa, Australia, and parts of Europe. This tiny sea slug is well-known among divers, swimmers, and surfers in those regions because while small, it packs a mean punch.
The Blue Dragon feasts on physalia (“blue bottles”), velella velella (“little sails”), and the stinging cells of porpita (“blue buttons”), all surface creatures that are blue in color. They have been documented to preform acts of cannibalism when food is in short supply. Most interesting, however, is the Blue Dragon’s tendency to prey on the Portuguese man-of-war, a highly toxic siphonophore that can kill prey much larger than the small Blue Dragon. Instead of being affected by the stings of the man-of-war, the Blue Dragon ingests the stinging cells and convert the venom for its own use. This may be possible due to hard disks in the skin of the slug or the secretion of mucus, similar to the clown fish’s immunity to anemone stings. The dark structures that branch from either side of the slug’s body store the venom for personal use which can make the Blue Dragon’s sting more dangerous than that of larger venomous creatures.
Glaucus atlanticus is closely related to glaucilla marginata, a smaller blue sea slug that is sometimes mistaken for the Blue Dragon. The words glaucus and glaucilla mean “color of the sea” in the titles of these nudibranchs. Both species have similar behaviors and diets, as well as the blue coloring of the skin. Glaucilla marginata, however, is found only in the Pacific Ocean, has a greater number of cerata, and a longer tail length than that of the glaucus atlanticus. Due to their venomous nature and particular diets, both are not to be touched in the wild. Neither species has been successfully kept in captivity, making them unadvisable aquarium pets.
While beautiful and unique, these creatures are best viewed from a distance. The Blue Dragon’s sting will leave you burning and wishing you had respected its space.