26/07/2019
A new study has discovered that butterfly numbers have decline by a third in the United States over the past two decades, echoing declines observed across Europe.
Tyson Wepprich of Oregon State University and his colleagues consulted volunteers at the Ohio Lepidopterists, a society that has been collecting weekly data on butterfly sightings across the state over the past two decades.
Wepperich explained: "We analysed their data to estimate trends for 81 species over this time and found that many more are declining than increasing. Overall, the number of butterflies you'd expect to see has fallen by 33 per cent, or at a rate of 2 per cent per year."
The overall declines reflect those witnessed across Europe, where well-established citizen science projects such as the currently ongoing Big Butterfly Count have documented contractions in both range and abundance of many species, including 'generalist' butterflies that should thereotically be more resistant to decline.
Given that butterflies are used as a proxy for studying insects, the worrying trend also raises alarm bells about the health of other insect populations across North America.
As temperatures increased, Wepprich and his team found that species from the south moved north into Ohio and were growing in number, while numbers of more northerly species dropped away.
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