There's a sea-slug that eats the venomous Portuguese man o' war. What does it do with the poison?

It’s no secret that some species of animals have developed incredible means of survival. The diversity of life in the ocean alone is difficult to fathom. Hence, there always seems to be an inexhaustible supply of interesting facts to learn about marine biology, and the blue glaucus (Glaucus atlanticus) is a perfect case in point.

Even though it is often mistaken for a jellyfish, the blue glaucus is distinct in a number of ways. This sea slug characteristically floats upside down near the surface of the water. How do they manage to do it? By swallowing air, which is then stored in their stomachs, giving them the ability to float.

That’s not even their most unusual quality. They survive mainly by eating hydrozoans (tiny animals living in salt water), including the Portuguese man o’ war . . . even the stings! In fact, not only do the stings provide sustenance for the blue glaucus, but they use the poison for their own defense.

For obvious reasons, this species has been of serious interest to scientists for as long as they have been known. They were first discovered by Westerners on Captain Cook’s second voyage to the Pacific. Scientists who accompanied him on his journey first described the animal in 1777.

(Source)