Funny thing -
I'm looking round the garden this morning and see a butterfly, a Red Admiral on the bird table. Surely it's not eating crumbs. Maybe it's on the way out and has flopped there. I approach the table and the butterfly takes off. So I continue walking round, then I turn and see the butterfly is back. Now it's on the inside of a bowl of water and looks like it's taking a drink. This is weird!
I go over to the table and see that there's something in the water - a pigeon feather? A closer look informs that it's a large moth and the butterfly seems to be touching it with it's nose, or whatever protrudes at the forward end of a butterfly. I take hold of the bowl and the butterfly's off again. I drop the bowl on the grass to get rid of the mucky water and the dead creature, and what do you know? 'Dead' creature starts to flutter about the ground.
What can I do? Nothing, is my decision. I leave the moth (or is it a colourless butterfly?) to dry out survive or perish, or make a meal for a passing bird. Well, I couldn't take it to a vet and I don't know any hospital for lepidoptera.
Later my missus goes in the garden and sees that the Red Admiral is back and on the grass keeping the moth company.
Sad end to strange tale; the moth died and it's companion disappeared.

How to explain? I can't. Insect solidarity? Empathy? Altruism? I'm stumped.

Correction (6.9.14): The butterfly was not a Red Admiral but a Peacock, the missus tells me.