My two monarch caterpillars are growing steadily. I check on them many times a day.
First, the question of names. I quickly rejected lame ideas like Tweedle Dee and Tweedle Dum, or Jeckyl and Hyde. Liz suggested Juan and Juanita, because they could end up wintering in Mexico. But those names didn't ring my bell. Since the little guys are monarchs, I decided on King George (the one we kicked out of North America), and Queen Elizabeth I.
Both have been through their first molt--the shedding of skin--to allow for growth. I think I can see the ghostly film of their shed skin, but it's too tiny and filmy to be sure. George is much bigger than Elizabeth--perhaps that's because he hatched a day earlier.
I'm now feeding them a new leaf every day. I wash out their metal bowl at the same time, to keep things sanitary and prevent disease (because they aren't bowl-trained). They don't yet eat a whole leaf, but they quickly eat some large holes. I change the leaf to assure they have fresh food and that they don't dry out, since they get their water from their food.
I'm careful not to touch the larvae directly--they could easily be crushed. To transfer them to the new leaf, I cut a tiny triangle from the old leaf with the caterpillar included, then place the piece of old leaf on top of the new leaf. If I bump the little triangle to dislodge the larva, he falls a short distance, then lowers himself down to the new leaf on a thread of silk.
Behavior of the larvae
Since the little guys are eating machines, at first glance they don't seem to have any behavior except eating and "frassing." (Frass is the term for insect excrement--little dark pellets.) But there are subtle things they do.
Though I place them on the top of the leaf, they always go to the underside of the leaf. Obviously, on the underside they are protected from sunburn, drying out, and predators. Since the larvae incorporate the poisons of the milkweed, they are well-protected from most predators. Their handsome black, green, and yellow stripes are a warning coloration--like the black and yellow stripes on a yellow-jacket.
They also seem to have periods of activity inactivity. So far, I haven't seen them active at night. It's not clear why they wouldn't eat around the clock, to grow as fast as possible. When inactive, they may be preparing to molt.
I wonder how they would behave if they were blown off their home plant? They cannot survive on anything except a plant of the milkweed genus. Would they search for a new milkweed plant, or climb any stem they came across? Perhaps their best option is securing themselves to the home plant with the strands of silk I have seen. If they fall, probably they just climb the silk back to the home plant.
It's amazing that--contained within each tiny larva--are the complete instructions for the instinctive behaviors of BOTH the larva and the adult butterfly.