The Blue Glaucus, also known as the blue dragon or sea swallow, is a striking marine mollusk with vibrant blue and silver coloration. This small sea slug measures about 3 centimeters (1.2 inches) and has a flattened body with six appendages that branch into finger-like cerata. Floating upside down at the ocean’s surface, it uses a gas-filled sac for buoyancy, allowing it to drift with ocean currents. Its blue underside faces upwards, blending with the ocean’s hue, while its silvery-grey dorsal side faces downwards, camouflaging it against the bright surface.
Primary Prey
The Blue Glaucus primarily eats other pelagic, venomous creatures that float on the ocean’s surface. Its most notable prey is the Portuguese Man o’ War (Physalia physalis), a siphonophore known for its potent stinging cells. The Blue Glaucus also preys on other stinging organisms like the by-the-wind-sailor (Velella velella), and the blue button (Porpita porpita). These prey animals are suitable food sources because the Blue Glaucus possesses an immunity to their venomous nematocysts.
Acquiring and Utilizing Prey
The Blue Glaucus feeds uniquely on venomous prey. It uses its muscular foot to hold onto the tentacles of its victim while feeding. The slug has a specialized radula, a ribbon-like structure covered with serrated teeth, which it uses to scrape off and ingest parts of its prey. This process allows the Blue Glaucus to consume large chunks of organisms, even those significantly larger than itself.
The Blue Glaucus absorbs and stores the undischarged stinging nematocysts from its prey in specialized sacs called cnidosacs, located at the tips of its cerata. This process, known as kleptocnidae, allows the sea slug to repurpose the venomous cells for its own defense. The Blue Glaucus can select and concentrate the most potent nematocysts, enabling it to deliver a sting that can be more powerful than that of its original prey.
Ecological Role and Human Interaction
The Blue Glaucus preys on venomous siphonophores, regulating populations of these surface-dwelling organisms. Its ability to consume and concentrate the stinging cells of its prey makes it a formidable predator in its ecosystem.
For humans, interaction with a Blue Glaucus can result in a painful sting. Since the sea slug concentrates the nematocysts from its venomous diet, touching one can cause symptoms similar to or more severe than a Portuguese Man o’ War sting. These symptoms can include intense pain, nausea, vomiting, and skin reactions like redness and papules. Even after a Blue Glaucus has died, its stored venom can remain active, making it unsafe to handle. Avoid touching these creatures.