You may have heard that one rumor about cutting earthworms in half. That, if you split ‘em straight down the middle, they’ll grow into two new earthworms?

Yeah…that’s just a myth. Please don’t do this.

Earthworms can regenerate their tail end if it’s cut off, but they still won’t regenerate into two separate worms. Damage from the clitellum (that larger segment in the middle) and above will kill the worm.

That said, while earthworms can’t be split into two separate worms, that doesn’t mean we the rumor is 100% false! There’s a kernel of truth to it…we’re just looking at the wrong worm. We need to turn our attention towards these little guys: an order of flatworms known as Tricladida…or more commonly, planarians.

Many flatworms are parasitic, but planarians are among the kinds that aren’t! Some of ‘em are even quite cute, with little rudimentary eyes and an adorably squooshy body. But that isn’t the only cool thing about them. They have amazing regenerative abilities, like recover-from-the-tiniest-fraction-of-their-bodies level. And yest, if split right down the middle, they’ll regenerate into two new li’l guys.

One more thing: if a planarian is only partially split, it’s possible for you to get one with two heads, as each half regenerates its own head! Kinda makes me wonder how their digestive system works in that case. Do they share a single digestive system? Considering how planarian digestive systems work, that could have some weird ramifications. Normal planarians don’t have an anus, they just have a single “blind sac” that both takes food in and excretes waste. So…the worst case scenario for our two-headed friends is…

…Probably best not to think about it.