LionFish says......
Well as far as I am concerned I hate Damsels. I wouldn't keep one in my tank for all the money in the world because they are a waste of time and money as they enjoy hurting other fish and when you try to catch them you have to tear the tank apart. Ha, I have a bunch of lionfish. I just drop my Volitan in the tank and the Damsels just seem to disappear! Wonder what happened there?
Anyways Damsels are quite aggressive little suckers. If you have a large tank you have a slim chance of catching it. If you really want to keep it you may have to just keep it by itself or get something to get rid of it for you. But, overall, damsels will pick on fish much larger than them so you will have to get rid of that little sucker. If you already have a Trigger, you must have an aggressive tank so get a lionfish and he can take care of the problem for you. Yes, Triggers are in general aggressive, but it is unusual for them not to defend themselves. If the Damsel is that much larger than the trigger, it could kill it.