I thought it was "blind bird"= "three worms" but MacColl's comment floored me- as if it was a common motive. This is where I thought it came from- a standard stanza:

There is a bird on yonder tree,
They say it's blind and cannot see;
I wish it had been the same with me
Before I joined his company.

MacColl gave an analysis which make some sense, even tho I don't agree- it's basically:

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55. DIED FOR LOVE. There is a large group of love-lamentations which have enough verses in common to be called 'a family.' They are all based upon a man's infidelity to his avowed lover.

1. Deep in Love- "Must I go Bound"
2. Butcher Boy
3. Love has brought me to Despair-- "blind worm" motive
4. Waly waly
5. Tavern in the town "Let him go, let him tarry" The alehouse verse is vital to this type.
6. Careless Love
7. Died for love
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He doesn't even mention Sheffield Park or Brisk Young Sailor. In my opinion, altho I'm just learning these ballads/song, only Tavern (which is a 1891 composition and not a folk song) and Butcher Boy are closely related.

What do you think?

Richie