Interesting behaviour on Saddleback Butterfly fish

[howdy20012002]

hello all
I just recently brought in a few saddleback butterfly fish and have noticed a very interesting behaviour.
they hover over hermit crabs and rub up against them.
they do this for a few seconds at a time.
I have all noticed all 3 showing this behaviour in 3 separate tanks.
the other butterfly don't show this behaviour yet all the saddlebacks do.
any clues what this is about?
I was thinking something liking a symbiotic behaviour somehow where a crab cleans them??? i dunno if there is a crab like that or not.
that is what this behaviour sorta of reminds me of.
anyone have any experience with this?
thanks for the input in advance
Neal

[Delphinus]

No idea myself but would agree that is interesting. Try to catch it on video if you can!

Saddle butterfly, aka Chaetodon ephippium? I've always liked those. Please share some pictures even if you can't get the video of the crab scratching.. :)