I think a bird -or even a crow in particular- would make a great mascot (or at least has one of the biggest mascot potentials).
And while I’m absolutely not favouring a jelly fish, I just want to mention, there is a crystal jellyfish which would fit name-wise probably the best (I’m still in favour of a bird though - which could be still justified just fine by @beta-ziliani’s explanation by its attraction to shiny things).
The idea of a beetle is unique and has potential that other programming language mascots do not have. The negative meaning of the word " bug" might also be nice thing. We need to come up with some better explanation as Rust means fungus. However, since beetles are generally complex in shape, it would take more artistic talent than a crow to make it a friendly mascot. I feel that crows will certainly succeed. However, the attraction I feel for crystals is more like that of a powerful, shiny beetle than a clever crow.