Tiny and Tough

These are two sets of photos of two monarch caterpillars that hatched in early December; let's call them Tiny (the horizontal) and Tough (the vertical). Tough spends a lot of time on dried twigs and pods, feeding on that material and sometimes migrating to greener foliage further down on the milkweed plant. Tiny has spent all its time on greener leaves, but for a period of a few days did not move at all. I thought maybe it was dying, but about a week ago it started moving and feeding again. The first photos were taken 10 days before the 2nd. Both caterpillars are now about 2 cm long and 3mm wide. When I touch them, they don't seem to notice and their little bodies feel very cold.