Why are insects thriving in England’s rivers?

Researchers have studied insects in English rivers for thirty years. The Environment Agency monitoring data shows that insects and other invertebrates are increasing and it may be linked to lower levels of metals in the rivers, such as zinc and copper.

The New Scientist magazine (19 May 2023) reported that insects are more abundant now than at any time over the past thirty years. 

Research scientists at the United Kingdom Centre for Ecology and Hydrology collected samples of insects using nets at 1,515 sites around England from 1989 to 2018. Scientist Andrew Johnson says that insects from a range of different species have increased in both urban and rural rivers. ‘You could argue that our rivers are our greatest environmental success story since the war,’ he said, referring to the second world war.

They analysed 45 different variables, such as chemical levels, physical factors, and temperature, and found that zinc and copper levels were the trends most frequently linked with increases in insect diversity. Metals, such as zinc and copper, can affect the reproduction cycle of insects.

The metals come from wastewater sources such as soaps, meat, and shellfish. They were reducing partly due to the introduction of European Union wastewater regulations, which requires companies to remove more contaminants before releasing wastewater into rivers. Another reason for the reduction of metals in rivers is the decline of coal burning in England.

Insects are increasing, but the increase depends on location and region. Not all rivers show the same results. In addition, Andrew Johnson says that data also shows that other animals are decreasing – such as salmon and eels. He says monitoring the water quality of the rivers in England, and the insect count, will continue to provide information on the situation.  

Photographer: Martina Nicolls 

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