US butterfly populations have plummeted in the last decade

If you'd had the feeling that you see fewer butterflies than you used to, you're probably right. 

A new study published in the journal Science has revealed that butterfly populations in the US have plummeted in the last decade. 

Researchers analyzed 12.6 million records of butterflies based on over 76,000 surveys conducted all over the US. Between 2000 and 2020, total butterfly numbers fell by 22% across the 554 species counted. 

The US-based research follows global trends in butterfly population losses in recent years. 

"Comparable declines are being recorded in all European nations where rigorous monitoring has occurred. Similar losses are no doubt occurring globally wherever land-use is intensifying," said Jeremy Thomas, an ecologist at the University of Oxford, UK.

US butterfly populations in decline

The researchers analyzed data from 35 monitoring programs across the US. 

The analysis found that numbers of individual species of butterflies, like the Monarch butterfly, had plummeted. One third of all US butterfly species have declined per year over the past two decades. 

For every species that was said to have increased, 13 others are said to decline.

The declines were nationwide, but hotter and dryer regions of the US were hit worse than more northern climates. Butterfly populations in the midwest, southwest, and southeast regions reduced by 21-55% over 10 years. 

Why are butterfly populations declining?

Research has shown that butterfly populations are declining globally due to climate change, habitat loss, and the use of pesticides in agriculture.

Rising temperatures and more volatile weather patterns have created multiple threats for butterflies. Research has shown that butterfly migration routes and habitats have been disrupted.

"The main driver of butterfly declines is intensive modern land use. Modern agriculture eliminates almost all species where crops or sown grasses are grown," said Thomas.  

Urbanization, agricultural practices and deforestation have reduced butterfly habitats and flower populations, endangering the survival of butterflies and other insects.

Increased use of pesticides, particularly neonicotinoids, has also been linked with falling populations of pollinating insects, including bees and butterflies. 

Neonicotinoids are insecticides primarily found in pesticides used on crops, flowers, and even flea medicines for pets. Neonicotinoids are nicotine-like chemicals that affect the nervous system of insects.

Conservation efforts can strengthen butterfly numbers

Conservation efforts are proving effective at boosting butterfly numbers, at least in some local areas.

"Much can be achieved locally in nature reserves and other protected areas, provided they are managed in ways based on a sound ecological knowledge of their ecological requirements," said Thomas.

"Fortunately, unlike many vertebrates, a whole population of butterflies can exist on a very small area of land whenever this is managed in the best way possible."  

Local conservation efforts in the UK have seen some success boosting butterfly numbers. 

"We are working with farmers and other landowners across the UK to create and restore valuable butterfly habitat and we are having fantastic results on a small scale," said Richard Fox, Head of Science at Butterfly Conservation, UK.

Fox said one effective conservation method that's boosting butterfly numbers is creating more habitats for butterflies to live and feed.

"In South-West England we have borrowed a local farmer's hairy Mangalitsa pigs and English Longhorn cattle over the past year to trample down thick bracken and create more space for dog violets which are the food plant of the endangered High Brown Fritillary butterfly," said Fox.

With good management and conservation efforts, Thomas said a great deal can be done in nature reserves and other protected areas to reverse the overall trend of falling butterfly numbers.

Edited by: Fred Schwaller