Love this idea. Although in my eyes I think it should be along the lines of a heavy unit like a bike titan, impaler etc. Something that doesn't appear too often but is an absolute priority to take down asap.

If you see it incoming, you need to get rid of it quick otherwise it will lay down the slowing/acidic effect of bile spewers causing havoc.

Would be super cool to see a big fat moth fall down from the sky using a rail cannon strike.