www.ukbutterflies.co.uk

The received wisdom is that flight times today are some two weeks earlier than they were 50 years ago. However, I don’t think it’s quite as simple as that.

Woodland species, eg White Admiral, Purple Hairsteak, PB and SPB Fritillaries are undoubtedly earlier. So too are those that are restricted to particular habitats, eg Silver Studded Blue. But are the more “generalist” species (wide choice of habitat) really flying any earlier today? I have in mind for example Orange Tip, Peacock (the summer emergence), Small Copper, which give the impression (to me at least) as being on the wing are more or less the same time as they have always been.

Now those species that are flying earlier today seemed to have made that jump forward rather abruptly and relatively recently. To return to the example of White Admiral (and also Silver Washed Fritillary). In the early 1970s the peak emergence was perhaps mid-July whereas today, although still flying in mid-July, many individuals show signs of being quite elderly (before the question is raised, I am talking about the same geographical areas). So when did that jump forward occur?

This link gives mean temperatures but it would need a lot of study to be able to make interpretations. The only trend that is reasonably apparent is that (this season of course the exception) is that the months November to March have been warmer in recent years.
http://www.metoffice.gov.uk/research/ha ... ET_act.txt

Discuss.

Jack

Jack, I don't think these variations can be relied upon. Back in the 1950s when I had more time to spend looking for things ~ in Gloucestershire I saw both Orange Tips and Duke of Bs in late April 1954; White Admiral females already slightly worn on 21st June, 1957 and Pearl Bordered Fritillaries in huge numbers during the first week of May 1959 ~ a very fine summer with months of daily warm sunshine IIRC. Some of the really old books mention the "April Fritillary" so I do not think the trend is anything more than cyclical ~ although I strongly suspect Global Warming is a racing certainty but that does not mean early warmer temperatures and more sunshine everywhere all the time ~ indeed it can mean the opposite in certain places and conditions ~ more rain and cooler temperatures a lot of the time.

IIRC, the early 1970s saw mainly rainy/cooler summers ~ I remember finding fertile Purple Emperor ova and newly hatched larvae on the sallows in the second week of September... Oh yes, and very freshly laid ova the last week of August ~ being that monocolorous green before showing any signs of fertility which they usually do by colouring up within 48 hours of being laid.
...

Cotswold Cockney:

...is a racing certainty...

Appropriate turn of phrase for you John! With your career background, you should be an expert on statistical analysis, so just the man to look into flight times, etc.

We ought to meet up next summer. That "secret" reserve of yours sounds fascinating.

Jack

In other words - given the right environment, with stable and suitable weather, many butterflies can respond by developing quickly and even double-brooding should a run of seasons, or a single particular season or locality be particularly good? Or they will emerge and be seen later when cooler weather delays development?

Put bluntly - weather and habitat conditions permitting - they'll come out when they are good and ready!

Not much blooming help in trying to book my precious holidays from work so I can target SSB in Portland or Lulworth Skipper in Dorset or High-Brown in Devon, is it?
If I pick the wrong week, I may not see them at all or they may be so tatty, I'll miss the chance to get some good shots, knowing my recent luck

( full-time worker still paying the mortgage!)