These are a great friend to have in the garden or pastures if you have Tansy Ragwort. This is a highly toxic plant to most livestock, and all parts are toxic.
The little Tansy Cinnebar Moth larva are voracious eaters of tansy ragwort, both leaves, buds and blooms. The will also feed on other members of the Senencio plant family, including groundsels, dusty miller, and butterweeds, but the tansy ragwort is its favorite food
I have never had it damage or feed on any of the other plants in my yard.
Here is a tansy plant that manged to hide until this week. It was the bright colored Tansy Cinnabar Moth larva that caught my eye.
Here is the moth. Sorry the photo isn't very good. I will try to get a better one to replace this one.