I am happy to say it is one of the not very common "3-D" range of "hovering butterfly" weights made by Salvador Ysart.
The design, with the insect set above a green ground, and two outer rows of canes, together with the partly ground pontil mark (not "polished" as in the eBay description), fits well with others that I have handled. I am aware of at least two others where the butterflies have what appear to be plain colour wings (but which may be formed from flattened simple millefiori canes).
Some people may consider that such weights were from the pre-war years and therefore fall into the "early Monart" category. My own thoughts, based on the visual evidence, lean heavily towards the 1940s period of Vasart (Ysart Brothers works).