The blue glaucus, also known as the blue dragon or blue sea slug, is a visually striking marine creature known for its potent sting. Understanding its defense mechanisms and habitat is important for coastal safety.
What is a Blue Glaucus?
The blue glaucus (scientific name Glaucus atlanticus) is a type of mollusk, specifically a nudibranch or sea slug. It measures around 3 centimeters (1.2 inches) in length, though some individuals can be slightly larger. Its body is flattened and tapers, featuring six finger-like appendages called cerata.
This creature exhibits a distinctive coloration, with a silvery-grey dorsal side and a vibrant dark and pale blue ventral side, sometimes marked with dark blue stripes on its head.
The blue glaucus is pelagic, meaning it inhabits the open ocean, primarily floating on the surface of tropical and temperate waters across the Atlantic, Pacific, and Indian Oceans. It maintains buoyancy by holding an air bubble in its stomach, often floating upside down. This inverted position, with its blue side facing upwards, helps it camouflage against the ocean’s surface from aerial predators, while its silvery underside blends with the water’s bright surface when viewed from below.
How They Acquire and Deliver Potent Venom
The blue glaucus is not inherently venomous. This sea slug feeds on other venomous marine organisms, such as the Portuguese Man O’ War (Physalia physalis), by-the-wind-sailors, and blue buttons. It is immune to the toxins of these prey animals.
Instead, it consumes and stores undischarged stinging cells, known as nematocysts, from its prey. These nematocysts are concentrated in specialized sacs (cnidosacs) at the tips of its finger-like cerata. When threatened, the blue glaucus releases these stored cells, delivering a sting more powerful than that of its original prey. Even after death, these stored nematocysts remain active and can deliver a sting.
Symptoms and First Aid for a Sting
A sting from a blue glaucus can cause immediate pain, itching, and redness at the site of contact. Some individuals may experience more widespread reactions, such as nausea, vomiting, or acute allergic contact dermatitis. In more severe instances, a sting can lead to allergic responses, difficulty breathing, dizziness, or a widespread rash, and in rare cases, anaphylactic shock.
If stung, it is important to rinse the affected area thoroughly with saltwater rather than fresh water, as fresh water can cause more nematocysts to discharge. Avoid rubbing the area, which can also trigger further venom release. Applying heat, such as immersing the stung area in hot (but not scalding) water for about 20 minutes, can help to deactivate the venom and alleviate pain. Any visible stingers should be carefully removed using tweezers or the edge of a credit card. If symptoms are severe, persistent, or worsen, seeking immediate medical attention is advisable.
Where to Find Them and How to Stay Safe
Blue glaucus individuals are found in tropical and temperate ocean waters worldwide, drifting with ocean currents. Strong winds and currents can often wash these creatures ashore, sometimes in groups referred to as “blue fleets.”
To remain safe, it is important to avoid touching blue glaucus specimens encountered on beaches or in the water. Even if they appear to be dead or harmless, their stinging cells can still deliver a painful and potentially dangerous sting. The general rule of “look but don’t touch” is paramount when encountering these creatures. Educating children about the dangers of handling these attractive but harmful animals is also a sensible precaution.