Can One Earthworm Become Two?

I'm sure everyone, at some point in their life, has heard that if you cut an earthworm in half, both halves have to potential to survive as independent entities. Sounds pretty cool! But is it true?

Earthworms are pretty remarkable creatures. They have an amazing ability to regenerate much of their bodies. Let's say you were to cut an earthworm in half. The front portion of the worm should include the mouth and a part called the "clitellum," which is the slightly broader un-segmented part, seen clearly in the photo below. Additionally, your cut should include at least ten segments more after the clitellum.

In this case, if you have made your cut in the proper location, the front half of the worm will indeed regenerate and become a whole worm once again. However, the back end of the worm is not viable, and will die. The mouth and the clitellum, which is where the worm's reproductive organs are, are vital to the worm's functions. Without them, there is no chance for survival.

However, while they are not "earthworms," there are some species of flatworm, known as "planarians," that are indeed capable of becoming two separate individuals after being bisected. In this case, the flatworm is split down the middle. Two two halves in some species of flatworm are able to regenerate and become two separate, living flatworms.

Polycelis felina, a freshwater planarian

Sources:

Moment, Gairdner B. (1942). "Simultaneous anterior and posterior regeneration and other growth phenomena in Maldanid polychaetes". Journal of Experimental Zoology 117: 1. doi:10.1002/jez.1401170102

"Gardening with children – Worms". BBC. Archived from the original on 2014-04-28.

Reddien, Peter W.; Alvarado, Alejandro Sanchez (2004). "Fundamentals of planarian regeneration". Annual Review of Cell and Developmental Biology 20: 725–57.


Photos:

"Earthworm". Licensed under GNU Free Documentation License 1.2 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Earthworm.jpg

"Regenwurm1" by Michael Linnenbach - first upload in de wikipedia on 09:58, 16. Feb 2005 by Michael Linnenbach. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Regenwurm1.jpg

"Polycelis felina" by Eduard Solà - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Polycelis_felina.jpg