How can weather radar detect swarms of mayflies?

Weather radar systems, such as those used by the National Weather Service, are designed primarily to detect precipitation by measuring the intensity of echo signals reflected from particles in the atmosphere. Because mayflies often emerge in massive swarms—sometimes numbering in the billions—these dense clouds of insects reflect radar signals in a manner similar to rain or other forms of precipitation.12

Consequently, these swarms are frequently detectable on weather radar displays. While the radar is intended to track meteorological phenomena like storms or wind patterns, the sheer biological density of a mayfly swarm creates a significant enough echo to be captured and identified by the system.21