Ever wonder how earthworms regrow or survive dissection? It is one of those weird/bizarre things in nature which fascinate me. Here is a pretty comprehensive story detailing all you would ever want to know about the topic, including worms that only reproduce through this self-mutilation, akin to a masochistic mitosis.
Making heads or tails out of severed earthworms
The red wiggler, or compost worm, might regenerate a new head or a new tail, depending on where it suffers amputation.
Loss of any of the first 8segments might result in a complete regeneration of the head.
The worm might grow a new head if cut behind the 13th segment, but it can’t replace sexual organs.
A separation between segments 20 and 21might yield a new tail for the head and a new head for the tail — a possible two worms.
The first 23 segments are roughly the limit for partial head regeneration by the cut-off tail. A loss of more than that might result in tail segments at both ends — and a dead end for the worm.
A cut-off head might regenerate a partial tail if separation occurs in front of the 55th segment. Behind the 55th, full tail regeneration is possible.
Eisenia fetida
Source: The Biological Bulletin
Every gardener has had the gruesome experience of plunging a spade into the ground, only to find that he has sliced anearthworm in half.
Will it die? Regenerate the lost part? Become two earthworms?
The answer depends on a variety of factors, including the type of earthworm and the location and tidiness of the amputation.
Scientists studying earthworms get mixed results even when using anesthesia and a scalpel, so sloppy surgery from a rusty trowel won’t do much for a worm’s chances for regeneration. However, worms can rebound from sacrificing some of their hundred-plus segments to a hoe or to a hungry robin or mole.
Regeneration of heads and tails commonly occurs when an injury activates stem cells that differentiate into replacement parts. Another transformation occurs when tissue suddenly finds itself closer to the front or back of a regenerating worm. Through a process of cellular reorganization, the tissue conforms to its new role in the worm.
The rules of regeneration
• Most earthworms can lose several segments from their head and grow them back. With the red wiggler, a worm often used in composting, the more head segments lost, the less likely they will be fully regenerated. The marsh-loving blackworm, however, always generates eight replacement head segments no matter where the worm has been bisected.
• The ability to generate a new tail is almost universal among segmented worms.
• An amputation between head and tail can sometimes result in two worms, with the front section growing a new tail and the severed tail growing a new head.
• Sometimes a severed tail generates new tail segments instead of a head. Like the rest of the worm, the twin-tailed creature absorbs oxygen from the soil and can stay alive for a while, but it’s unable to feed itself and will eventually perish.
• Severed red wiggler tails especially “have trouble mounting productive head regeneration and thus die of starvation and brainlessness, if you will,” says Mark Zoran, who studies nervous system regeneration at Texas A&M.
• A severed head made up of fewer than 20 segments can heal, but the animal tends to develop a dysfunctional lower digestive tract. Would it die of constipation? “I guess it is possible,” Zoran says, “but I doubt that little head fragment would be doing much eating while in such a state of disrepair.”
• If sexual organs are lost in an amputation,night crawlers can regenerate them, but red wigglers can’t.
The self-amputators
Temperature shifts can cause blackworms to develop a fissure between the head and tail, roughly at the 48th of its 150 segments. Each fragment develops a new head or tail, with each part forming a full set of gonads.
A not-too-distant relative of earthworms is the white worm, a tiny translucent worm that some people grow to feed to their aquarium fish.
One species of white worm relies exclusively on fragmentation to reproduce. It spontaneously fragments into five to 10 pieces, each of which grows a new head and tail. Sometimes, a fragment will grow heads at both ends, resulting in what scientists call a bipolar worm.
Michael Bradley - Time Traveler 
I’ve no plans to use this information for good or evil, but it still is very interesting to be aware of the process beyond the old “chop it in half and you’ll end up with two worms through regeneration” business.
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Pretty remarkable the variance between worm types as well. It does make you wonder how much sadistic trial and error was required to see the results by worm type of slicing them in each segment.
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I’m reminded of a New Yorker magazine cartoon from the 1930-1940s, where a Time magazine reporter’s writing about eating dog.
He starts out in the first panel typing something like “Dog meat is…”. In the next panels, you see him going to a restaurant where they kill and prepare a dog to eat. In the last panel, he returns to his typewriter, and writes “…slightly tough and stringy.” Or something on that order. Ha!
You are right. sometimes it’s best not to know how knowledge was acquired, and to hope not by what seems the logical answer of vermicide by serious if overly insensitive scientists more interested in an answer than the suffering of fellow creatures on this rock!
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Reblogged this on miftahulhuda234.
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