The oak tree on my father's farm is a place of repose for thousands of Monarch butterflies on their migratory path between Mexico and upper North America, a journey of up to 3,000 miles. The tree had more butterflies than leaves, opening and closing their wings as if the tree itself was breathing.
The caterpillars lived off the milkweed growing in the fields and ditches. Their skin is brightly colored, but birds stay away, as milkweed is poison to them. This website gives more information on their trip.