Anyway my gut feel approach seems to be backed up by more expert evidence. We've now had two poor summers on the trot. Rain forces butterflies to find shelter and prevents them foraging for the nectar they need for a good breeding season. Ideally what they want is sunny weather with just enough rain to help flowers grow.
Apparently butterfly numbers have been in decline since the 1950's with intensive farming fueling the use of pestiscides. Wet summers therefore compound the problems.
According to Butterfly Conservation Chief Exec Dr Martin Warren:
There is no doubt that it has been dire for most species and unfortunately it follows an already bad run of summers.
We are really concerned about the small tortoiseshell which has been in long-term decline and which seems to have reached a trough and stayed there."
and from Matthew Oates, National Trust nature conservation advisor:
Weather conditions impact greatly on the fortunes of butterflies. The last two summers have been blighted by rain and wind that seriously affected their fortunes across the UK.
Yet some species have managed to overcome the odds and have had excellent flight seasons. Overall, though, it has been a dreadful butterfly year, probably the worst in my 45 year experience.
I've kept detailed records since 1972, and it's certainly the worst year since then. My previous lowest tally of small tortoiseshells by mid-August was about 250, in 1988. This year I've counted 20.