Lapwings behaving like terns (!)

[Tursiops2]

Spent a couple of hours sitting at Kingsfleet this afternoon. In a field to one side of the river was a flock of a dozen or so Lapwings and about a hundred Black-headed Gulls. Every so often, the Lapwings, and a few gulls, would take to the wing and fly out over the river, where they would start to bank and turn, and make low passes over the water for ten or fifteen minutes at a time, for all the world like a flock of Black Terns, before returning to settle in the field.

I know Lapwing flocks are always restless, often taking to the wing and flying around for no obvious reason, but I've never seen behaviour quite like this before. It was certainly not a response to disturbance or a predator. They were a bit too far away to be sure, but they looked very much like they were catching insects on the wing. There were also fish frequently leaping from the water as well.

Has anybody else seen behaviour like this? What sort of insects would be emerging from a slow-moving, non-tidal river at this time of year?

Coincidentally, on the way there, I walked through a massive swarm of Craneflies, obviously a mass emergence, but this was about half a mile from the river.

T2