Was there a pale dorsal patch on the last segment, like in http://lepidoptera.butterflyhouse.com.au/acro/leucomelas.html Please: can your rear it to get an adult, to verify its species ?
No pale patch apparent on any of the caterpillars (I added a photo of one). Rear them to adult? hmmmm... they are munching their way through our Convolvulus which we grow for seed production, BUT since you asked so nicely, and for the sake of science, I will adopt a couple and see what they turn into :)