More about Monarchs

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This one's for @JudyEv. First of all, if you really want to read the definitive book on monarch butterflies, read "Chasing Monarchs" by Robert Michael Pyle. I met Bob Pyle several years ago and was amazed by his in depth knowledge. His book follows a migration, from the northern part of the US all the way down to Mexico where they winter over. Here are some facts about monarch butterflies. The caterpillars grow up eating milkweed pods, which are toxic to most creatures. They store the toxin inside them, making taste awful to predators. When they emerge from the cocoon, they need the pressure and struggle of getting out to fully form their wings. The wings need that squeezing to force the blood into the little vessels all through the wing, which makes the wing pop out rigidly, ready for flight. A monarch who is helped out of their cocoon by cutting will never be able to fly. Only every fourth generation of monarchs migrates. The first three generations mate, lay eggs, their eggs pupate, and the pupae transform into butterflies but they only live six to eight weeks. The fourth generation is the one that migrates and lives for six to eight months. They are the ones who reach Mexico. The research is not clear on this, some sources seem to indicate that all generations migrate but they each just go successively farther. The research is still evolving here. In total, monarchs can migrate up to 2500 miles and fly at speeds of 12 to 25 miles per hour. They complete another four generations through the winter till this next fourth generation is the one to fly back north, to the milkweed pods up there. In flight, monarchs can move the different fluids around in their body to shift their weight as they use up their fat reserves. This helps them fly more efficiently. Personally, I didn't know that about the four generations thing - I learned that researching for this post. That would explain why we saw a mating flight the other day! Previously I'd thought they did all their breeding up North.