Every year, millions of these beloved flutterers fly en masse from Canada and the U.S. to wintering grounds in Mexico, pollinating fields and farmland along the way. In fact, the roughly 3,000 mile journey makes theirs the longest migration of any butterfly species on earth.
But the sighting of this swarm isn't just notable for having been picked up on radar, it comes at a time when monarch butterflies have been in decline due to habitat loss and herbicide use in their fragile breeding grounds. For the last two decades, the species' numbers have fallen dramatically, from as many as a billion to just around 35 million last winter.
The loss of this species could spell trouble for American agriculture. Three-fourths of all crops in the U.S. rely upon pollinators, like monarch butterflies - making them not only one of the most beautiful creatures on the planet, but also one of the most essential.