I have a red fly on my lilies. Does this kill the plant or can I treat it.

Sounds like lily beetle, best to pick them off and stamp on 'em, inspecting daily before they get a chance to lay their eggs, which look like bird poo up and down the stems. There are sprays available, but lilies with open flowers should not be sprayed - the treatment kills pollinating insects like hover flies, ladybirds and bees too

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I think you missed a sentence Bamboo. the eggs are about 2mm longand dull red/brown laid under the leaf. the grubs look like bird poo/spatters of soil. the grub covers itself in its own poo to make it unattractive to eat. that strategy seems to work very well.!

agree about picking off and squashing them. when I find grubs the leaf gets cut off and the grubs swilled in water before being feed to the pond fish. they love them.

You're right, I did miss out the stage between egg and grubs... but to be honest, I've never noticed the eggs, only ever noticed the problem at the bird poo grub stage, which I suspect is true of most of us...

Be aware that when you go to pick them off they sometimes fall to the ground when they often land upside down and as they are brown underneath they are then hard to see.