This is the [very large] caterpillar that was climbing up the carport wall this weekend. It will eventually become a Western Tiger Swallowtail Butterfly, which are by far the most impressive butterflies we get here in Los Alamos.

The caterpillar made several trips up and down the wall and is now missing, so maybe the plywood roof of the carport didn't suit its needs. But we got to examine it closely as it made its way along the wall. The dark stripe that runs along the back is actually a long internal tube called the dorsal vessel which contains the heart and pumps blood out around the caterpillar body. You could see pulses of fluid traveling along it from the back to the front at a rate of about 0.5 Hz. It was really cool.