What animal has the weirdest pee? There are so many to choose from.
Male Amazon river dolphins flip onto their backs and pee into the air, creating an arc of urine that lands somewhere near their head. Not competitive urination, but a rich and literal stream of chemical information, which other dolphins may then swim through.
Male porcupines wee on prospective mates because it helps the females to become sexually receptive, while Siberian chipmunks apply bits of gnawed snake urine to their bodies to help disguise themselves from predators.
When it comes to the actual content of the urine, however, there’s only one winner. Reptiles, as you may already have surmised, produce urine that is solid.
When animals digest food, proteins and nucleic acids are broken down and ammonia is produced as a waste product. This can be toxic to cells, so it has to be removed.
Aquatic animals, including most bony fishes, excrete this directly into the water. Mammals, meanwhile, convert ammonia into a less toxic substance called urea, which they excrete in their urine.
But reptiles, insects and birds, convert their ammonia into uric acid, which is non-toxic but almost insoluble in water. This makes the urine that they produce solid, semi-solid or paste-like.
Take a peek under a microscope, and you can see that the uric acid is made of tiny crystals.
In a 2025 study, published in the Journal of the American Chemical Society, researchers collected pellets of urine from more than 20 reptile species and studied them in the lab. All of them contained spheres of uric acid salts.
The spheres of ball pythons, Angolan pythons and Madagascan tree boas produced uric acid salts made of tiny textured microspheres. These varied in diameter from 1–10 micrometres, making them roughly the same width as a strand of spider silk.
X-ray studies further revealed that each microsphere is made up of even smaller nano-sized crystals, made of uric acid and water. Because these nanoparticles are so small, they have a high surface area relative to their volume.
They also have a slight negative charge.
These two features make the nanoparticle able to associate with positively charged salt ions. So, as well as helping them to manage levels of uric acid, the nanoparticles also help the animals to regulate their salt balance.
The process is thought to have evolved as a way to help reptiles and other animals that live in dry environments conserve water. Now, researchers think we could learn a thing or two from them.
Humans produce small amounts of uric acid, which we excrete in our urine. Sometimes, however, this can build up. When it accumulates in the urinary tract, it can cause kidney stones. When it accumulates in the joints, it can cause gout.
Studying the mechanisms that reptiles use to process their uric acid could one day lead to treatments for related human disorders.
So, whilst reptile wee may be weird by our standards, it’s normal for them, and one day we may all be thankful for it.
This article is an answer to the question (asked by Brendan Wood, Leicester) 'What animal has the weirdest pee?'
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