Song the Eleventh

I finished listening to The Grim Grotto today. Stellar as always. For the sake of the world (and one Bananabasket in particular), here are the lyrics to the song on the recording, which reinforces the undercurrent of biological warfare that runs through the book:

A million mushrooms fill the field
Where marchers' bodies lately fell
More marchers marching heavy-heeled
Release more spores that march as well

Across the twilit charnel grounds
And over long bewildered farms
Through palaces where not a sound
Is heard - though there should be alarms

The winter comes and only ice
Is crushed beneath the marching feet
In all the land where once was rice
There now is nothing fit to eat

Except mushrooms, which nourish not
The body; nourish not the mind
And often poison eating rot
The marchers march insane and blind

Ahh, the Gothic Archies, bringing nightmares to children since 1999.

I have the strangest feeling I've read this as a poem before - especially the second stanza and the last line. Can anyone tell me what it is?