The precipitous loss of native vegetation across the United States has led to a dramatic decline of insect populations. This year, for or the first time in memory, the monarch butterflies didn’t come, at least not on the Day of the Dead. They began to straggle in a week later than usual, in record-low numbers. Last year’s low of 60 million now seems great compared with the fewer than three million that have shown up so far this year. Some experts fear that the spectacular migration could be near collapse.
Native to the West and Midwest of the Americas, monarchs travel on an annual migration through Canada, California and Mexico, pausing along the way to gather in enormous flocks of tens of thousands of butterflies. They gather in such incredible numbers that trees appear to be draped in orange-and-black leaves, which upon closer examination resolve themselves into fluttering wings.
Think of the monarch butterflies’ population as the output of a machine process that has gone wrong. To understand that process, scientists have had to observe the butterflies and their environments for decades. It was only in the 1970s when Canadian entomologists Fred and Nora Urquhart discovered that their migration spans 3 to 4 generations, with each new generation completing only part of the circuit between Canada and Mexico.
The butterflies who begin this incredible cross-continental migration in Canada will never make it back – only their great-grandchildren will.