Along the Mississippi River swarms of emerging mayflies have been seen on radar. The radar and image below are from a July 11, 2017 emergence near LaCrosse, Wisconsin. On the radar you can see the mayflies emerge from the river and head toward the north.
This image was taken in LaCrosse during the emergence.
Radar & Image Source: National Weather Service
Is it possible that other swarms have or can be tracked by weather radar?
Bird migration has been studied by Weather radar Bird migration study using weather radars and the monitoring can be visualized here - Bird migration density profiles. A github site Time Integrated Multi altitude Migration Patterns has been developing algorithms to estimate the density, speed and direction of migration movement at different altitudes around a radar.
Swedish scientists have used the Movable Atmospheric Radar for Antarctica to detect birds, which showed up in their radar echo. I remember that they were talking about teaming up with ornithologists to use what for them is noise (as they're interested in the middle and upper atmosphere) as a signal, but I don't know if they got anywhere with that. Although not a weather radar, I find it a lovely example of scientific serendipity.
This Weather Channel story gives a lot of things that show up on NWS radar... such as bats
Or even vehicles on the highway:
I believe the conditions typically have to be just right atmospherically to track things in the low atmosphere like this, generally involving beam ducting due to inversions most common near/after dark. So it's probably unlikely they could be used to do any continual analysis. But they're definitely neat images!
But indeed radar reflects varyingly depending upon the wavelength it sends out (NWS is about 10 cm) and the properties of the item it hits, so there are all kinds of current/potential applications for radars, from geology to medical applications to tracking space junk.
