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Climate change to blame for monarch butterfly’s recent decline

A female monarch butterfly (Danaus plexippus) laying eggs on a milkweed plant

Corry Anne / Alamy Climate change has been the biggest cause of the precipitous decline of the monarch butterfly ( Danaus plexippus ) in North America in recent years, say researchers who fear parts of its breeding range will become inhospitable under future warming.

The puzzle of the decline of the insect, famous for its epic migration from the US and Canada to Mexico in the winter , has been variously blamed on herbicides wiping out the milkweed plant their caterpillars exclusively feed on, to problems on their migratory route and climate change.

To empirically test which is having the most impact, Erin Zylstra at Michigan State University and her colleagues combed 18,000 mostly citizen science surveys of monarchs carried out in the US and Canada and combined them with weather data to build a model of their populations. Between 2004 and 2018, the amount that rainfall and temperature deviated from long-term averages was nearly seven times more important than other factors in explaining the monarch’s summer numbers.

“Yes, climate change is happening. It looks like it’s affecting monarchs. Now we have this information, we can have a smart plan for […]

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