Julie Zickefoose: A Caterpillar Sheds Its Skin

Down at the Monarch Ranch, the caterpiggles were gettin' fat, poopin' and eatin', poopin' and eatin'. When they get this big and fat, they'll soon go on walkabout, looking for a place away from the milkweed patch where they can hang themselves up, shed their caterpiggle skin, and burst forth as a chrysalis. You have to pounce on them when they get big and fat if you want to be part of the process. This'n's ready to harvest.

We bring them inside and install them in a small terrarium, where we put a fresh milkweed top in a narrow-necked vase of water to provide food. They eat like crazy for a couple of days and then wander around, finally pasting themselves to the top of the terrarium with silk. Here, the caterpillar is creating the liquid silk pad that will harden and suspend it for the next couple of weeks. The head end is to the left. It can be hard to tell with monarchs which end is which. I think the silk comes out of spinnerets in the rear end.

Once secure, the caterpillar hangs upside down in a J shape, waiting for the transformation to chrysalis. Slowly, the caterpillar's brilliant yellow, black and white skin becomes dull and translucent. The first sign that something's going down is when the antennae, normally mobile and responsive, get all limp and crinkled.

See how the antennae on the head are just hanging here, no longer turgid?

Here, I must stop and give credit to Phoebe, who watched this caterpillar like a hawk, and kept it with her so she wouldn't miss the moment when it split its skin to emerge as a chrysalis. She noticed an undulating motion as the caterpillar hung there, and the skin started to stretch and pile up at the fastening point at the rear. Suddenly it split down the back like a pair of my old skinny pants.

From there, things progressed quickly, and the undulating wave of the chrysalis' still pliable body sent the skin rumpling up into a pile at the rear end of the creature.

Seeing this glorious, fantasmagorical thing emerge from the dulled skin of the caterpillar was awe-inspiring.

More and more stripes and abdominal segments are visible with each wriggle.

I especially love the next shot, because Phoebe's sweet red lips are blurred in the background. At this point we're all whooping and hollering, and I'm frantically shooting around both kids' heads as they crowd in to see the miracle.

Look at the blue, gold, and white stripes!! Who knew?

Now the chrysalis changes its dance, with the undulating wriggle becoming a wild spiral hula as it moves the skin up and off its body.

In the picture above, you can see the proto-wings of the butterfly-to-be, folded like shields over its body.

A few more wild loops, and the skin pops off-ptoo! to land on the vinyl tablecloth, creepy legs, antennae, and jaw parts intact. The chrysalis won't be needing those jaws any more. Transformed to a sucking straw, they'll be.