[Lewis Thomson (OP)]

Ruomei has sent in this question for us to unpick & find answers to.

"This evening  my son and I reread the book "Dairy of a Worm" by Doreen Cronin. One of our favourite lines was when the little earthworm told his big sister "no matter how much time she spent looking into the mirror, her face will always look just like her rear end". After laughing at that, my son asked why does an earthworm's face looks similar to its rear end. When i couldn't provide an answer, he settled down to an explanation of himself: earthworms need to tunnel both forward and backward, that is why both ends look similar.  I admit it was a nice explanation, but might not be the right one. Does an earthworm actually tunnel backward?
Later my husband voiced his opinion: it is understandable to have symmetry in the body, it is much simpler. We should ask why the faces and the rear ends don't look alike for many other animals.  I disagree, two of the main functions of the faces and the rear ends are "input" and "output", it makes sense that the two "ends" evolve into different forms. But we still can't answer my son's original question."

Can you help them? Leave your answers down below...

[Origin]

Earthworms do not look the same at both ends.  If you google earthworms and look at a picture it would be clear to you too.  Your son was correct that their ends do look similar and they do in fact move forwards and backwards through tunnels.

[alancalverd]

Mature earthworms are hermaphrodite, producing  sperm towards one end and ova towards the other, so (a) they have to be able to recognise each other's front from back in order to reproduce and (b) they can't be brother and sister!

[Bored chemist]

Why does an earthworm look the same on both ends?
Because you are not looking carefully enough.

[ruomei]

Mature earthworms are hermaphrodite, producing  sperm towards one end and ova towards the other, so (a) they have to be able to recognise each other's front from back in order to reproduce and (b) they can't be brother and sister!

Thanks, It is nice to know. How do they know the other earthworm is not a brother or sister? by chemical/pheromone?  I assume the same goes with snail which is also hermaphrodite?

[ruomei]

Why does an earthworm look the same on both ends?
Because you are not looking carefully enough.

This is not very helpful, isn't it? One can't expect a question from a 5-year old reading a children's book carries the same rigor as in a science paper. One can easily change out "the same" to "similar", and the question would still be interesting and maybe amusing.  Or you just want to post a smart-read-end answer? 

[Bored chemist]

How do they know the other earthworm is not a brother or sister?

What does it mean to be a brother or a sister?
How would you define that with a hermaphrodite?

One can easily change out "the same" to "similar", and the question would still be interesting and maybe amusing.  Or you just want to post a smart-read-end answer?

Welcome to the forum.

As far as we can tell, the 5YO asked the right question.

my son asked why does an earthworm's face looks similar to its rear end.

But whatever adult posted it here asked the wrong question.

Did you spot that?

[alancalverd]

Relax, chaps! The story was amusing but sadly has fallen among pedants.

It's easy to criticise Cronin for being unobservant, but at the same time she should be applauded for entertaining at least one real kid and exercising the minds of three boys who never grew up (every scientist is a Peter Pan at heart) in this forum.

And full marks to said real kid for asking a penetrating question, plus a star for Dad's effort: the bilateral near-symmetry  of animals gave Alan Turing much food for thought.

IIRC earthworms always tunnel forwards but make a vertical U-turn to bring their heads to the surface to eat.

Meanwhile I heard a great line from a woman interviewed in a serious (Radio 4, anyway) program about twins. She said "When I get dressed  to go out I think "I could be really beautiful", then I look at my sister and realise I couldn't.

[ruomei]

How do they know the other earthworm is not a brother or sister?

What does it mean to be a brother or a sister?
How would you define that with a hermaphrodite?

One can easily change out "the same" to "similar", and the question would still be interesting and maybe amusing.  Or you just want to post a smart-read-end answer?

Welcome to the forum.

As far as we can tell, the 5YO asked the right question.

my son asked why does an earthworm's face looks similar to its rear end.

But whatever adult posted it here asked the wrong question.

Did you spot that?

User name checks out, i wonder if one is so bored that one has to come to this forum for a bit excitement from berating others.
Only after I graduated from my Ph.D. did i realized how nitpicking can often kill curiosity and creativity and thus make things less interesting.
Happy trolling!

[ruomei]

did a bit googling after reading the first a few responses. a few articles indicate that earthworms do move backward, albeit less preferred action ([url1][/https://biologyjunction.com/earthworm-facts/], [url2][/https://sciencing.com/how-do-earthworms-move-13406972.html])