As the discussion goes on - and very interesting too! I thought I would post a sequence of sawfly images.
1. 16-04-2007 Egg laying.
We had loads of saw fly laying eggs last year on the undersides of willow leaves. The male took a very protective stance while the female was laying the eggs and if I got too close dive bombed me. The whole process took a couple of hours.
2. 23-04-2007 Shows the eggs hatching, even here their little tails shoot up.
3. 24-04-2007 These hatchlings are one day old, and have already started to change colour and are eating their way through the first leaf.
4. 09-05-2007 This sawfly larva has grown to 2.5cm.
I am not sure which type of sawfly they actually are.