The blue dragon, also known as Glaucus atlanticus, is a unique sea slug found drifting on the surface of temperate and tropical oceans worldwide. This small mollusk, typically reaching about 3 centimeters (1.2 inches) in length, possesses a flattened, tapering body with six appendages that branch into finger-like cerata. Its striking coloration, featuring dark and pale blue hues on its underside and a silvery-grey dorsal side, serves as camouflage, helping it blend with the ocean’s surface from above and the bright sky from below.
Primary Food Sources
The blue dragon is a specialized predator, primarily feeding on venomous marine organisms. Its most notable prey is the Portuguese Man o’ War (Physalia physalis), a highly venomous siphonophore. By consuming these creatures, the blue dragon acquires their stinging cells for its own defense. It also preys on other pelagic cnidarians such as the By-the-Wind Sailor (Velella velella) and the blue button (Porpita porpita), and can consume the violet snail (Janthina janthina). The blue dragon’s ability to feed on such potent prey stems from its immunity to their venomous nematocysts.
Ingestion and Digestion
To consume its venomous prey, the blue dragon employs specialized mouthparts, including a chitinous ribbon called a radula. This radula is equipped with serrated teeth, which, combined with a strong jaw, allow the sea slug to grasp and tear off pieces of its prey. The blue dragon ingests significant portions of its prey, including the stinging cells, known as nematocysts. Its digestive system is adapted to handle these cells without triggering their discharge. The slug can consume entire organisms or large chunks.
Venomous Defense
The blue dragon repurposes the stinging cells of its prey for defense, a process known as kleptocnidae. After ingesting nematocysts from its venomous diet, the blue dragon transports these undischarged stinging cells through its digestive system. These nematocysts are then stored in specialized sacs called cnidosacs, located at the tips of its finger-like cerata.
The blue dragon concentrates these stored nematocysts, making its own sting potentially more potent than that of its original prey. When threatened, the blue dragon can release these concentrated stinging cells as a defense mechanism. This unique adaptation allows the blue dragon to protect itself without producing its own venom.