Wagtails skating on thin ice

We have had a few cold nights recently with frost and ice on puddles.  On a cold afternoon I noticed this pied wagtail (Motacilla alba) hunting on the ice.

It is a pity I didn't shoot a video as it was struggling to keep its feet.

Then I noticed a grey wagtail (Motacilla) a metre away on the ice.

It was also slip slidin' away, as Paul Simon would say.

I was surprised there was anything there for them to eat.

But then the grey wagtail found an enormous caterpillar.  Quite what that was doing in the ice I don't know.