Davy wrote But if gnats, why were they hunting over the surface?

We may be having a word association mix up here.
Biting and blood sucking gnat-type critters are called
mosquitoes on the North American side of the pond.

The term gnat, in the UK, seems to cover all sorts of
critters, which I found out from the first website I found
-http://www.gardensafari.net/english/mosquitoes.htm
(I just love the internet)

Gnats, here, are a number of non-biting bitty flies.
They do not feed.
Their time over the pond is spent flirting, courting, mating and
laying eggs in water or on aquatic vegetation.

Usually, non-feeding gnats, or small flies, hatch out
and swarm over the pond, do their duties, set the next
generation in motion and fall to the pond to get snapped
up by fish or
become a handy fast food stop for
dragonflies and birds.

k :-)