It's an annual migration, Doc. Every year, Monarchs head south to Mexico to breed, go to tea parties, and generally consort frivolously with one another. Then they come back up here and lay their eggs on milkweed plants, if they can escape getting run into by trucks.
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Yellow and black butterflies everywhere, a huge cloud of them swarming across I-40 in the western part of Arizona. An invasion perhaps, an evil plot to make the Arizona desert a happier place or, just a nightmare induced by lack of sleep...
BTW, Monarchs are orange and black. The big yellow and black ones are tiger swallowtails and are loners, ie. they don't group together to migrate.
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