I think some "chigger" songs started off as something else. The original verses of OH, SUSANNA in the database might offend, so this is what I found in Ronald Herder's 500 Best-Loved song Lyrics:

When I jumped aboard the telegraph
And travelled down the river,
The electric fluid magnified
And killed five hundred chigger.

When the bullgine bust, the horse run off,
I really thought I'd die,
So I shut my eyes to hold my breath,
Susanna, don't you cry.

Seems to fix the song pretty well, without being TOO euphemistic.
-Joe Offer-