Findings: Skilled fliers hitch a ride

July 5, 2002

This month, 3.5 billion insects weighing a metric tonne in total biomass will fly over an area of Britain the size of Hyde Park, writes Steve Farrar.

The extent of entomological air traffic in British skies has been revealed by specially developed vertical-looking radar.

The study has revealed not only the quantity of insects but also their sophisticated navigational skills.

Scientists from Rothamsted Radar Entomology Unit discussed their work at the Royal Society's summer science exhibition this week.

Project leader Jason Chapman said the research shows for the first time how insects behave when they take to the skies.

"The sheer abundance of insects over Britain is amazing," he said. "But the major surprise is how organised insect flight is."

The radar operates 24 hours a day under the control of a PC, which also analyses and displays data. It transmits a narrow, conical beam of 3.2cm waves from a marine radar vertically into the sky.

The transmission is kept in a constant state of flux, with the plane of linear polarisation rotating and the beam centre wobbling in a small circle. This means that the back-scattered signals from insects moving into the beam between 150m and 1,200m in the air can contain much more useful information.

Computer analysis of this data can reveal the speed and direction of movement of each insect, its alignment, mass, body shape and wing-beat frequency.

Dr Chapman said that long-term monitoring of the skies over southern England has found that insects fly concen-trated in dense layers. This may be because they are hitching a ride on air currents.

"Some groups of insects will all head in the same direction, sometimes at an angle to the wind, which suggests that their navigational skills are more sophisticated than previously thought," he said.

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