How big a butterfly? I'd say a C-Stand is the minimum, and maybe a Junior or Combo stand would be preferred. Butterflies become sails in the wind. And you want some weight on them. For anything bigger than a 6x6, I'd have two junior stands with 35# sandbags on them. And maybe some wind anchors.
I'd go for beefy-babys instead, granted you have to buy a c-stand head for it, but it'll work out just fine.
I just never really like using c-stands for holding silks, just always feels a bit janky. Junior stands with lollipops for anything bigger is definitely the way to go, and definitely get sand bags and some rope for when it gets windy.
Other thing you might want to do is practice your knots. Truckers hitch, bowline, and clove hitch are all essential knots that become very useful for tying silks down.
Stop. Unless you are hanging a 4x4, you need to use a combo stand. Even then, a combo stand is designed to hang those types of things. A c-stand is designed to hang small lights or flags, but really nothing bigger. If you care about safety, you'll get the right tool for the job.