Is it climate change?

What species would you choose to monitor climate change?

The question is frequently asked but, as the discussion develops, people seem less and less sure that an increase or a decline of taxon x or y has anything to do with climate change at all, either directly or indirectly.

So, we want to hear from you as to the species common or rare you might (we stress might) monitor on a long-term basis to see if their fortunes had anything to do with global warming, or cooling, increased storms, tidal surges and so forth.

Does the arrival and northward spread of the wasp spider (Argiope bruennichi) have anything to do with warmer summers, milder winters, an increase in grasshoppers, or did it simply hitch a ride across the Channel and spread across England just because it is here?

The first UK record for this species was from Rye in East Sussex in 1922, so it has taken a long time to get going. But maybe it has been introduced more than once and it is only the more recent arrivals that have managed to spread. Is this likely to have anything to do with climate change or not? And if it is, how can we prove it?