As I remember it, talk of a decline in the UK butterfly population was pretty big in the 1970s, and it was always blamed at that time on loss of habitat, such as the disappearance of wild flower meadows.
I did a bit of Googling and found an organisation called "Butterfly Conservation", which is supposedly the world's largest research institute for butterflies and moths:
The organisation "was formed by a small group of dedicated naturalists in 1968 following the alarming decline of many beautiful butterflies". The webpage doesn't mention climate change at all. The President of this organisation since 1998 turns out to be David Attenborough. It confirms my impression that butterflies were in decline long before AGw came along.
David Attenborough's role in promoting climate change awareness and alarmism is interesting. He suddenly announced that he was highly concerned about climate change back in May 2006, and claimed that prior to that he had actually been an AGW sceptic, as described in this newspaper article:
But it seems implausible to me that somebody like Attenborough would have been a sceptic for many years, and was able to keep that view quiet, given the kind of people he is going to mix with. My rather cynical guess is that following the BBC seminar on climate change held in January 2006 (the 28Gate seminar), it was decided that Attenborough's documentaries were going to start to feature warnings about climate change, taking advantage of Attenborough's status as an authority figure. There was however a slight problem in that Attenborough had not previously mentioned the issue of climate change in his documentaries, so they needed an explanation for the sudden change, and came up with the story that he had previously been a sceptic and had only become convinced of the threat posed by AGW in 2006.