What is this please?

[Terri]

I purchased a plant today called "Bishop Weed - Snow on the Mountain", I was told that butterflies were drawn to it. As it turned out they showed me two caterpillars feeding on the plant so I figured yea, something else besides monarchs. I have searched for hours trying to figure out what they are with no luck. This is the best photo (so far) taken through a dark screen room. These cats move like an inch worm. Does anyone know what these are? I'm nervous because the plant is in the screen room with all my monarch chrysalis.
Thank you for your help,
Terri

I hope the photo shows up

[Mona Miller]

http://forums.gardenweb.com/forums/load ... 14213.html
Info on invasiveness.

http://www.nhm.ac.uk/jdsml/research-cur ... ort=Family
The caterpillar host plant database list one lep and it is a moth: Agonopterix clemensella

[Terri]

Mona,
Thank you very much for your quick reply. I stopped by the nursery on my way home today to ask if I could exchange it (they don't take returns) since I just bought it yesterday. The salesman told me monarchs will eat it, I kinda doubt it but I figure what the heck for $8 I'll keep it in a pot away from other plants so it won't spread.
On a happier note I came home to 7 new monarchs which I'm going to release as soon as I take some pictures.
Thank you again,
Terri

[Mona Miller]

They may have meant that the adults use it for nectar? They definitely don't use it as a host plant.