The black swallowtail caterpillars were busy eating the forgotten fennel herb plants in a garden - there were several good size plants and a small cluster of a dozen caterpillars happily eating away.  The smallest caterpillars I saw (looking very closely) are mostly dark in color with a white 'saddle' in the middle and spiny. This caterpillar was probably between 1/4 and 1/2 inch - very small. While I was working on photographing these small caterpillars, I was also busy shooing away a wasp that appeared to want my subject for breakfast!

As the caterpillars grow up, they change some in coloration.

Then when they are nearing full size and will soon begin the pupae stage of life, they look similar to a monarch caterpillar with some variations.

I haven't yet found the pupae stage to photograph, so that's on my bucket list! But once they complete this stage they become a beautiful black swallowtail butterfly.