We have been watching our milkweed plants for Monarch caterpillars, and finally found three this morning. The largest was about an inch and a quarter long, and the other two were barely an inch. All three were happily munching away, well hidden in the long branchy stems of the milkweed.
You wouldn't think that something with bright yellow, black and white stripes would be hard to notice. But at this small size, those narrow stripes combine visually and make the caterpillars look greenish from a distance. The stems of the milkweed are also greenish, so the caterpillars are actually well camouflaged. As they get bigger, those bright stripes will be a warning to would-be predators that these caterpillars are not very tasty.
We took some pictures before heading to work, and then checked on the caterpillars again that afternoon. We re-found three caterpillars, and they were all noticeably larger. If these are the same caterpillars, they have grown considerably in less than ten hours.