MadSci Network: Zoology

Re: If you cut an earthworm in four pieces, will it stay alive?

Date: Mon Dec 7 09:56:11 1998
Posted By: Ruth Allard, Conservation Biologist, American Zoo and Aquarium Association
Area of science: Zoology
ID: 911248540.Zo

Dear Ms. Starr,

As with most answers to science questions, the real answer is 'it depends.' 
My first thought is, why do you want to cut an earthworm in four pieces?  
Why not two, or five?  Depending on how you cut the earthworm, part of it 
will either survive (not all four pieces will) or the whole thing will die.

Earthworms are annelids, or segmented worms.  Nightcrawlers, the big wiggly 
worms often used as fishing bait, have about 150 segments, while manure and 
red worms (red worms are also fairly common) have 95 segments.  Different 
segments perform different functions, just like our body parts.  We don't 
expect an arm to do what a toe can do, and the same thing is true for the 
segments of a worm's body.

Here's a great site with tons of worm info, and lots of drawings of 
earthworm anatomy:

Regarding your real question:  Earthworms run into this problem all the 
time, since birds like to eat worms.  When a bird tries to yank a worm out 
of its burrow, the worm uses bristles on its skin to hang tight to the wall 
of the burrow.  If the bird pulls hard enough, it can yank off part of the 
worm's body.  If the worm is broken off at the first seven or eight rings, 
it can grow new segments and will survive.  If the worm is pulled in half, 
only the head end grows back.  

So, if you cut a worm into four pieces, you most likely won't get four 
happy worms.  If you cut a worm into two pieces, you may get two worms, if 
you don't cut too far down the worm (only 7 or 8 segments down).  If you 
cut the worm in half, you'll get one live worm after the head end grows 
back, but the stress of being chopped in two may kill both ends.  I'm 
guessing that being split in half is hard on the poor thing.  

This information came from the following worm site, which has all kinds of 
details about earthworm anatomy and natural history:

If you really want to experiment with regeneration, I suggest working with 
planaria, which are a kind of flatworm.  They're generally very small, so 
it's harder to see everything happening (a magnifying glass helps), but 
they can regrow after many divisions.  I remember a junior high experiment 
in which we cut a planarian in three pieces, and the head and tail parts 
grew back quickly and were healthy, but the middle section was always 
sluggish, even though it regrew a head after a few days.  

A side note, just because this is my favorite worm story:  Charles Darwin 
was a big fan of earthworms, and spent a lot of time and energy studying 
their behavior.  He wanted to know if earthworms can hear, so he set up a 
box of earthworms and played various musical instruments at them to see if 
their behavior would change in response to a tin whistle, an oboe, or a 
bassoon.  His hypothesis was that if they heard in a high frequency, they 
might move in response to the tin whistle but not the bassoon, or vice 
versa.  I read about this experiment in a book by David Quammen, and would 
like to know more about this work because it makes me smile.  Can you 
imaging playing drums for a box of worms?  

I hope this helps answer your worm question, and encourages you to learn 

best regards,


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