After years of declining populations, there's happy news of a bright spot for butterflies.
In both the United Kingdom and pockets of North America, butterfly numbers are bouncing back. For some species, this population news signifies that 2019 was their best year for growth in more than two decades, according to the journal Butterfly Conservation.
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Regardless of location, the butterfly populations that experienced the most growth benefited from unusually warm and wet climate conditions. These ideal circumstances resulted in a greater number of caterpillars that successfully cocooned and lived through their immature stages of development to emerge as healthy adult butterflies.
In North America, for example, the 2019 count of monarch butterflies after their migration from Canada to Mexico revealed a 144 percent increase in population over the previous year. And, in the U.K., one of the species that exhibited substantial population growth in 2019 was the marbled white butterfly, which rose by 66 percent, according to Butterfly Conservation.
For some geographically restricted populations, the population boom may have saved them — for now — from extinction. The lulworth skipper, one of the U.K's smallest butterflies, is found primarily along a stretch of coast in southwest England. This diminutive flying insect in shades of moss green, burnished copper and charcoal has experienced plummeting population numbers in recent years. However, in 2019, its population rose 138 percent.
In addition to favorable weather for butterfly development, experts point to intensive conservation efforts in recent decades. Much of the work by volunteers and nonprofit organizations, such as butterfly waystations and education efforts, has turned around long-term population decline for some butterfly species.
While this is great news for butterflies — and the people who admire them — scientists warn that the war to save them isn't yet won. Take the monarch butterfly population native to California, for example. Despite the baby boom for their cousins overwintering in Mexico, California monarchs lost 86 percent of their population in 2019.
"We're really heartened to see a shift in the fortunes of many of our most-loved species," said professor Tom Brereton, associate director of monitoring and research at Butterfly Conservation in southwest England. "The long-term situation for butterflies in general does remain a cause of concern though, with more species declining than increasing since the 1970s."
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