Hello,
I believe that butter worms and sweet worms are the same. Butter worms have a sweet smell, very honey like.
Butterworms, also known as tebo worms, eat that one plant, and dont eat anything else. So what is usually done is they are just kept in the fridge (8-10C) untill ready for use. They go to sleep and can last for up to 3 months.
Butterworms are also treated before they leave Chile to prevent them from ever becoming a moth.
-Silkie