Took about an hour before they realized it was food. The littlest one figured it out first. Then the medium, finally the big guy. Before too long he'd chased everyone else away and was hanging upside down digging away at the bottom of the piece. You could hear the 'thunk' when he bit down on it.
Was fun to watch.
Of course today when I was feeding bloodworms he decided to come right up and take a bite out of my finger (must have looked like cantaloupe)...he has some tough pharyngeal teeth! Made me jump, which of course, made him fly away...

I'll have to try some watermelon this summer. <grin>