Swallows and Insects

These pictures are from Les Humphreys, who worries about this late nestful of swallow fledgelings.

As Les says, "It's a very long way to Africa," and all the other swallows have either left or look as if they're about to leave.

Les would like to know what these insects are. He has looked them up in his books, without success, and I'm unable to help him. There are thirty or more, all on the same plant.

Does anyone know what they are?

Many thanks, Les, for the pictures.