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Thanks again Nigel. I thought this might well be the case. At least I was looking at similar indicators to yourself with regard to differences between the two species.
I think I will have to give some serious thought about collecting specimens next year. Being so new to it I was thinking of leaving it until I had a really good grounding in the more common invertebrates, otherwise I'd end up needlessly collecting specimens of things that might be readily identifiable.
Maybe if I start with a small family, like Asilidae (in the UK), first?