copperband butterfly...

[Scorpion]

i've heard that copperband butterflies will eat aptasia... but when i talked to the person at the LFS were i got one, he said that they'll eat aptaisa if you starve them a bit. so my question is, are they known to eat aptasia only... or do they eat it as a last resort? also, i usually feed my tank frozen brine and the older inhabitants love it (2 clowns, 1 damsel, 1 cleaner shrimp). whenever i was at the LFS looking at copperbands (this was before my purchase of one a couple days ago), i noticed that the store feed them seaweed. are butterflies vegetarians?