A team of scientists combined 76,957 surveys from 35 monitoring programs and blended them for an apples-to-apples comparison and ended up counting 12.6 million butterflies over the decades. Last month an annual survey that looked just at monarch butterflies, which federal officials plan to put on the threatened species list, counted a nearly all-time low of fewer than 10,000, down from 1.2 million in 1997.
Many of the species in decline fell by 40% or more.
David Wagner, a University of Connecticut entomologist who wasn't part of the study, praised its scope. And he said while the annual rate of decline may not sound significant, it is "catastrophic and saddening" when compounded over time.
"In just 30 or 40 years we are talking about losing half the butterflies (and other insect life) over a continent!" Wagner said in an email. "The tree of life is being denuded at unprecedented rates."