Velella velella, scientifically known as the By-the-Wind Sailor, is a common sight in the open ocean and along coastlines worldwide. These small, distinctive marine organisms often wash ashore in large numbers, particularly during the spring and early summer months, covering beaches in a shimmering blue layer. Their sudden and widespread appearance frequently causes concern among beachgoers, who naturally wonder if these strange, jellyfish-like creatures pose a threat to human health or to pets. Understanding their unique biology is the clearest way to determine their potential danger.
The Stinging Capability of Velella velella
The direct answer to whether Velella velella is poisonous is that while they possess stinging cells, they are generally harmless to humans. Like all organisms in the phylum Cnidaria, they are equipped with microscopic stinging capsules called nematocysts on their tentacles, which they use to paralyze and capture small planktonic prey. However, the venom contained within these capsules is extremely mild when it comes into contact with human skin.
The nematocysts of the By-the-Wind Sailor are not powerful enough to penetrate the thicker outer layer of most human skin. Contact typically results in no reaction at all for most people, or at most a very minor, temporary skin irritation or slight itching. This reaction is not comparable to the painful sting delivered by true jellyfish, or their more venomous relative, the Portuguese man o’ war.
Identification and Unique Hydrozoan Biology
Velella velella is not classified as a true jellyfish (Class Scyphozoa), but is instead a colonial hydrozoan. The entire structure visible above the water is a colony of highly specialized polyps, all interconnected and dependent on one another for survival.
The organism is easily identifiable by its deep blue color, its small, oval-shaped float, and a thin, clear, triangular structure that serves as a perpendicular “sail.” This rigid, chitinous structure allows the animal to be passively propelled across the ocean surface by the wind.
Beneath the float, the colony consists of several types of specialized polyps, each with a distinct function. The central polyp, the gastrozooid, is responsible for feeding the colony after the prey is captured. Surrounding this are the specialized dactylozooids, which are equipped with the mild nematocysts used for stinging and defense. Reproductive polyps, called gonozooids, are also part of the colony structure.
Practical Guide to Safe Handling and Contact
Despite the low risk, beachgoers should minimize direct contact with stranded Velella velella. If you touch one, avoid transferring any residual nematocysts to sensitive areas of the body. You should immediately wash your hands with soap and fresh water, or rinse them thoroughly with seawater, before touching your face, eyes, or mouth.
If a slight irritation or rash does occur after contact, standard first-aid protocols for minor marine stings can be followed. The affected area should be rinsed with seawater, not fresh water, as fresh water can cause any unfired stinging cells to discharge venom. Applying heat to the area is the most effective treatment, so soaking the affected skin in water as hot as you can comfortably tolerate—around 40 to 45 degrees Celsius—for 20 to 30 minutes can help to neutralize the mild venom.
It is best to keep pets and small children from mouthing or playing with the stranded organisms. While the creatures are not toxic if ingested, the dried, brittle remains can still present a minor choking hazard or cause mild irritation to mucous membranes.
Why Mass Strandings Occur
The common name, By-the-Wind Sailor, describes the mechanism of the organism’s movement and eventual beaching. They are part of the neuston, the community of organisms living at the air-water interface, and are incapable of swimming against currents or wind. The clear, upright sail catches the wind, making their movement entirely dependent on surface weather conditions.
Their sails are angled either to the left or the right, causing them to sail at a slight angle to the prevailing wind direction. When sustained onshore winds, particularly during the spring, push the surface waters toward the coast, the Velella velella have no means to steer away. This results in millions of them being simultaneously driven onto the shore.
Mass strandings are often preceded by periods of warmer-than-average sea surface temperatures, which can lead to population blooms. Once swept ashore, they quickly dry out on the sand. The blue color fades, and the organisms become brittle, forming a fragile, cellophane-like carpet that poses no further threat.