Evening sky and a sawfly plague

A very hot day...chasing car insurance quotations for HL, cutting grass and stuff....then this evening as I was going out to water the vegetable patch, I noticed a strange noise - almost like light rain. Odd because it was in the mid twenties Centigrade even at half past eight. Then I noticed that the whitecurrant and gooseberry bushes seemed to have lost almost half their leaves. Closer inspection revealed several thousand (I don't think I am exaggerating) minute green larvae chewing away on the margins of the leaves. Nearly half the leaves of a large bush stripped in twenty four hours or so! The sound, I realised, was the noise of the dropping of the collective horde falling onto the weed suppressant fabric on the ground.....
So it has been an eventful evening collecting minute caterpillars by hand. I think I am going to have to learn about biological controls for next summer...bring on the nematodes!