These are two caterpillars I am rearing at home. I watched a monarch butterfly laying eggs on several milkweed plants on the very edge of an ATV/vehicle trail in Larose Forest a few weeks ago. I knew without a doubt that the milkweeds were going to be run over, so I brought both of the plants home, each with one egg. The top caterpillar is much bigger than the bottom one, though it is not easy to tell from the photos. It is about 1 1/2 times the size of the smaller one. It hatched within three days. The bottom one hatched after five days. Thus, the top caterpillar is 11 days old, the bottom one is 9 days old.