The charming animal that seems to be taken from a fairy tale and is capable of injecting us with poison

It's summer time, beach time. We swim, but we're not used to looking at other organisms that live in the sea, although we are aware that if we walk on the rocks with bare feet, we should be careful with sea urchin spines, and if we see something transparent floating, we know that it's most likely not a plastic bag, but could be jellyfish.

Climate change is causing organisms that were previously found only in tropical waters to now reach our shores. The Mediterranean has increased its temperature by about 2-3 degrees Celsius, and it doesn't seem so strange to hear on the news that they've glimpsed Portuguese caravels (Physalia physalis), whose stings are extremely painful and dangerous. In fact, Portuguese man-of-war are not a type of jellyfish or a single species, but rather a colony of different types of jellyfish and hydras that live together and share the duties of predation, flotation, and digestion. Some turtles, such as the black-fronted turtle, feed on them, but the fact that populations of these reptiles are declining also means they can now be found more easily on our coasts.

Another organism that eats man-of-war seems to be straight out of a fairy tale. It is the blue dragon (Glaucus atlanticus), a blue and silver sea slug with a fantastic design. It's also a tropical animal, like man-of-war, and its natural habitat is the warm waters of the Atlantic, Pacific, and Indian Oceans. It's even not uncommon to find it on the coasts of the Canary Islands. In the Mediterranean, however, it was once described more than 300 years ago off the coast of Ibiza, but for the past three or four years, some specimens have been found on the coasts and warmer waters of Murcia and Mallorca.

These fantastic animals measure between 3 and 4 cm in size. They are supported by the surface tension of the water and a gas sac inside, and they are carried by ocean currents. Curiously, they float upside down in the sea, and the electric blue lines running down their bodies correspond to the slug's feet. Seen from above, the bluish colors make it almost invisible in the blue sea water. However, their back is silver, an excellent camouflage to make themselves invisible to any organism looking at them from the ocean, as it blends in with the reflection of the sky.

Like many gastropods (snails and slugs) they have a raspy tongue that allows them to eat and tear off pieces of their prey, among which we find the gelatinous and poisonous man-of-war, of which the poison will be stored in its waxes (the kind of "fingers" that emerge from lateral outgrowths that, to our eyes, resemble hands).

This venom allows them to defend themselves from predators, but also forces them to undergo ventral fertilization. Gastropods are hermaphrodites and all individuals have both female and male sexual organs, therefore, they fertilize each other, generally in a lateral position, but blue dragons must do it face to face, anchoring their sexual organs and avoiding touching the "extremes", fertilize, they would end up poisoning each other.

So, as a summer tip, if you are lucky enough to see blue dragonets, admire them without touching them. They are not poisonous in themselves, but they can inject you with the poison they have accumulated from the jellyfish and man-of-war they have eaten, despite their charming appearance.