The insect census
Since April 29, 1964, a network of unusual towers has been continuously sampling the skies over the United Kingdom. These are the suction traps of the Rothamsted Insect Survey (RIS), a project that has created one of the world's most comprehensive long-term datasets on insects. Each of the 16 traps in the network—12 in England and 4 in Scotland—is a 12.2-meter-tall "upside-down hoover" that continually pulls air and any insects within it down into a collecting vessel. This specific height was chosen to sample insects undergoing long-distance migration high above the ground.
The survey operates two main networks. The suction-trap network primarily targets aphids, providing daily data during their main flying season from April to November. The second is a light-trap network, with around 80 traps across the UK and Ireland, which mainly attracts and samples moth populations. The light traps use standardized 200-watt tungsten-filament bulbs and are typically emptied daily by a dedicated team of volunteers.
Initially, the survey was established to help farmers. By providing warnings about the arrival and abundance of agricultural pests like aphids, the network allowed for more targeted pesticide use, moving away from the heavy prophylactic spraying common in the 1960s. Over the decades, the data has become an invaluable, impartial record of environmental change.
A long-term climate record
The continuous, standardized sampling has produced a dataset containing more than 50 million insect records. This long-term view has revealed significant shifts in insect populations and ecology. Analysis of the data shows that the total abundance of larger moths in Britain decreased by 33% between 1968 and 2017. The decline was more pronounced in southern Britain, which saw a 39% decrease, compared to a 22% decrease in the north.
The data also is a long-term indicator of climate change. The timing of insect life cycles, known as phenology, is a sensitive marker of temperature shifts. By tracking the first flights of certain aphid species, the survey has shown that spring-like conditions now arrive approximately two weeks earlier than they did in the mid-20th century.
The physical samples themselves are a unique resource. The survey has amassed a vast archive of collected specimens, which are available for further research. This collection allows scientists to perform new analyses, including genetic studies, on insects from decades ago, recording past ecosystems and the changes they have undergone. The RIS trap design has been so effective that it has been adopted in over a dozen other countries, creating a global standard for insect monitoring.