This week we're going to learn about animals that can regenerate parts of their body. What animals can do it, how does it work, and can humans figure out how to make it work for us too? Thanks to Maxwell of the awesome Relic: The Lost Treasure podcast for suggesting this week's topic! The planarian, not exciting to look at but you can get a lot of them easily: A starfish leg growing a new starfish, or possibly a slightly gross magic wand. Ping! You've been turned into a magical starfish: The adorable axolotl: The almost as adorable African spiny mouse: A hydra. Not really very adorable except possibly to other hydras but kind of pretty: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week’s episode was going to be about lungfish, but I had to postpone it because I ran across some conflicting information about a mystery lungfish, which required me to order a book that probably won’t arrive for a week or two. So when I tweeted about needing a new topic quick, Maxwell of the Relic: The Lost Treasure podcast suggested animals that can regenerate parts of their bodies. We’ve touched on regenerative abilities before in one or two episodes. Some lizards can drop their tail if threatened, which then regrows later—but a lizard can only do that once. The fish-scaled gecko from episode 20 can lose its scales and regenerate them repeatedly. But other animals can regenerate not just bits and pieces, but entire organs and even their brains. The sea lamprey can even regenerate spinal cord cells. You better believe researchers are trying to figure out how regeneration works and if it can be adapted for human application. A lot of worms can regenerate lost pieces, including earthworms. Whenever I’m gardening and accidentally cut an earthworm in half with the shovel, I reassure myself that the worm will regenerate the end I cut off. Some species can even grow back from both cut pieces, effectively turning one earthworm into two, depending on where it is severed, although that’s rare. Some species of worm can only regrow the tail, but some can regrow the head. And some, of course, can’t regrow anything. Leeches are a type of worm but they can’t regenerate at all. Planarians are flatworms. Some species live in water, some in damp areas on land, but they can all regenerate. If you cut a planarian in two, each half will regenerate into a new planarian. If you cut a planarian in three, you’ll get three planarians. Cut one into four, you get four planarians, and so on and on. Researchers with a lot of time and patience have determined that you can cut a planarian into as many as 277 pieces and you will get 277 planarians after a few weeks. But I guess if you cut a planarian into 278 or more pieces, some of the extra pieces won’t do anything. Starfish are well-known to regenerate lost or injured legs, and may even drop a leg to escape from predators the way some lizards drop their tails. Some species of starfish can regrow an entire starfish from a single limb. That’s oddly creepy. I don’t know why I find it so creepy. I don’t find the planarians creepy. It’s like if I was run over by a motorboat that chopped my arms and legs off, and instead of dying I not only regrew my arms and legs, my severed arms and legs each grew a new me. I don’t think I’d like that. Although I’m not going to get in the water so I doubt I’ll be run over by a motorboat, and also if I was, sharks would probably eat me before we could see if any parts regrew. Many starfish relations, such as sea urchins and sea cucumbers, can also regenerate body parts. When the sea cucumber is threatened, it can and will eject its internal organs. They’re sticky and full of toxins, which deters predators, and the sea cucumber just regenerates them. Most crustaceans, such as crabs and krill, can regenerate legs. So can spiders, which may drop legs to escape from predators.