Question
QUESTION: We have recently had a massive die off of earthworms in our front yard.  We have not added any chemicals/fertilizers.  It did rain lightly recently, but our neighbors do not have the same problem.  Is there something we can do to help our lawn/save our earth worms?

ANSWER: I know you state clearly, 'We have not added any chemicals/fertilizers', but I have to say a few of these things for the record.

First, U of Kentucky's Entomology Dept calls them 'thatch-busters':

http://www.ca.uky.edu/entomology/entfacts/ef402.asp

'Excessive Nitrogen applications that greatly reduce soil and thatch ph can be detrimental to earthworms. Earthworms are generally intolerant of acidic soils (pH less than 6.0).'  Yes, I realize you did not use chemicals or fertilizers, but some people might not consider Nitrogen a chemical or a fertilizer.  Also, do you know what the pH of your Soil is?  Earthworms endure pain and suffering in Acid pH; a pH of 4.0 will destroy one.

Do you have a heavy Clay soil that traps moisture and blocks air underground?

I could go on.  Let's stop there and please answer some of my questions.  Thanks for writing.

---------- FOLLOW-UP ----------

QUESTION: Thank you for info.
We did not use nitrogen, but I do not know the pH of my soil.
Yes, we do have clay soil (sod on top of clay soil, grass placed about four years ago.)
Thank you for your time and help.

Answer
I suspect if your Grass is healthy, the pH of the Soil is not the extreme acidity that would cause harm to the Earthworm population.

Clay however will trap water almost perfectly.  Which is why they make teacups and soup bowls out of it.

It sounds to me like you had enough rain to collect underground, trapped by the Clay.  Earthworms need Oxygen, too.  To avoid drowning, they head to the surface -- but if they're too slow, they are almost doa when they get there.  Add more rain after that, and it's curtains for the Earthworms.  This is my best guess, which I hate to say, but having looked high and low for a better explanation -- one that would satisfy me -- I think this is a case of drowning.

Any other theories, I'm all ears.  Thanks for writing.