First I must say, I know nothing about the butterfly bush. I did do a quick lookup on it though, and found this in a gardening section on iVillage. It is a response to someone asking if butterfly bush was toxic because they were thinking of getting one, but have a dog:
"Buddleja (butterfly bush) is an attractant plant toward hummers, but does not provide great amounts of nectar to hold them over. I definately give you the go ahead advice to put buddleja out in the landscape, but to really bring in the hummers, you need other shrubs and perennials to coax them into to give you are show and them a meal. Perennials like cultivars of Agastache, Salvia, Penstemon, Lonicera, Nepeta, Corydalis, Fuschia, and so on. Shrubs and trees like Aesculus Red Horse chestnut, Albizia julibrissin, Styrax japonica and obassia, Weigela, Ribes (selected) and so on. Buddleja is not toxic to the touch and ingested in small amounts, though it may, in large doses, can cause gastro-intestinal problems like vomint or diarrhea."
However, I also read on another site that the butterfly bush is actually a common name that can include several species. And in another site it briefly mentioned the butterfly bush as a plant that wild rabbits tend not to eat...which makes me wonder if they instinctively know it's not good for them. I'd take a bit of precaution with it, I think.
P.S. Also forgot to mention that on one site it stated that some varieties of the butterfly bush were being considered as being labeled noxious in some areas, because it has the tendency to spread and take over everything (kind of like purple-flowering loosestrife did in this area several years ago).
