This is what they looked like a week ago, on 8/31:
This is the third instar; the thoracic tubercules are spiky, but not actually very sharp, and they’re bright yellow.
Most of the time, this happens on a twig, and it’s very difficult to see – I’m lucky that this time, a couple of the caterpillars spun their silk pads on the side of the plastic container, and I could see what was happening!
If you look just in front of the caterpillar’s head, you can see the swirls of silk that it lays on the surface. It will then hook its feet into this silk, to help it peel out of its skin.
This is the same thing, viewed through the clear plastic. The silk pad covers the whole area that the caterpillar is standing on.
I didn’t see any in the process of changing, but this is what you get afterward – the shed skin is attached to the silk, and the caterpillar has walked out in its fancy new suit.
This is the fourth instar, with bright orange tubercules. I *love* the smiley face!
The knob at the back is still yellow.
Some of the larvae appear to be skipping the fourth instar, and going directly to the red-knobbed fifth instar skin. There are just enough that I can’t be absolutely certain these aren’t just a little ahead of the others – but they’re not all that much larger. We’ll see if they change again!