The Blue Dragon (Glaucus atlanticus) is a small, pelagic sea slug that draws attention due to its striking appearance and potential danger. This nudibranch, or shell-less marine gastropod, floats on the open ocean surface and is occasionally washed ashore. Despite its diminutive size, the Blue Dragon is capable of delivering a painful sting using a unique biological defense mechanism that concentrates the venom of its prey.
Understanding the Blue Dragon
The Blue Dragon typically reaches a maximum length of 1 to 3 centimeters. Its coloration provides sophisticated camouflage, exhibiting dark and light blue, silver, and gray hues. The slug floats upside down using a gas bubble for buoyancy, which reverses the usual pattern of countershading. The bright blue underside faces upward, blending with the ocean when viewed by aerial predators.
Conversely, the silver-gray dorsal side faces downward, helping it camouflage against the surface light when seen from below. Its body is flattened and tapered, featuring three pairs of branching, finger-like appendages called cerata. These cerata are specialized extensions of the slug’s digestive system.
The Blue Dragon spends its life drifting in the open ocean in tropical and temperate waters globally. It is a passive swimmer, carried along by the wind and ocean currents. This reliance on the elements means a group of them, sometimes called a “blue fleet,” can suddenly wash up on beaches following strong onshore winds, presenting a risk to people.
The Mechanism of Danger: Stealing Stinging Cells
The danger associated with the Blue Dragon stems entirely from its diet, as it is not inherently venomous. This sea slug feeds on other venomous, floating creatures, primarily the Portuguese Man O’ War (Physalia physalis). The Blue Dragon is remarkably immune to the powerful stinging cells of its prey.
This immunity allows the slug to consume the Man O’ War’s tentacles using specialized, serrated teeth. The Blue Dragon engages in a process called kleptocnidae, which is the stealing of undischarged stinging cells, known as nematocysts. These nematocysts are not digested but are separated and transported through the slug’s digestive tract.
The stinging cells are stored in specialized sacs, called cnidosacs, located at the tips of its cerata. The slug selectively stores the most potent nematocysts, concentrating the venom into its own body for defense. This concentration makes the Blue Dragon’s sting potentially more powerful than the sting of the Portuguese Man O’ War. When threatened, the slug releases these stored nematocysts, delivering a powerful defensive sting.
What Happens If You Touch One
Contact with a Blue Dragon, even one that has washed ashore and appears lifeless, can result in a painful sting due to the concentrated nematocysts stored in its cerata. The symptoms of a sting are similar to those caused by the Portuguese Man O’ War. An immediate and intense burning pain at the site of contact is the most common reaction.
This initial pain is often followed by a rash, blistering, or the formation of raised welts on the skin. Systemic symptoms can also occur, including nausea, vomiting, and a severe headache. In rare cases, a person may experience a serious allergic reaction, which can involve difficulty breathing or chest pain.
If a sting occurs, the immediate first aid response should focus on pain relief and deactivating any remaining venom. The affected area should be rinsed with seawater, avoiding fresh water, which can cause any remaining stinging cells to fire. Applying heat to the area is recommended, so soaking the sting in water that is as hot as can be tolerated for at least 20 minutes can help to denature the protein-based venom.
Pain medication like paracetamol or ibuprofen may be used to manage discomfort. Medical attention should be sought immediately if the victim shows signs of a severe allergic reaction, such as swelling of the face or throat, or if the pain is unrelenting.