www.ukbutterflies.co.uk

I would love to know where I could learn more about butterfly migration.
I have wondered for a long time whether painted ladies fly south later in the year or if they just perish up here. Similarly with red admirals. This year has been one of the best for a long time. Although numbers have declined considerably over the last month, there are still a reasonable number around. Do they really fly south? If they do, why do some appear not to, or are these ones from further north en-route?
I have so many questions!!! Why has it been such a good year for red admirals, yet so poor for painted ladies?

At the end of the summer of 2009, the year of the last big Painted Lady migration, it was pretty well established that there was a southerly outflux of butterfies. I believe the theory is that this is not usually observed because the movement south is at a greater height than the movement north earlier in the year.

Painted Ladies cannot survive our winters. Any influx we receive is dependant upon their breeding success during the previous winter - which they spend in North Africa. Red Admirals on the other hand, do appear to be able to survive British winters, even relatively harsh ones like the last couple we've had. Their numbers are topped up by continental immigrants, and it seems from this year that they too head south again. Why they have been particularly numerous this year is likely to be a combination of factors, including weather patterns (here and on the continent). They do not seem to be subject to the same degree of parasitism as their nettle-chomping relatives, possibly because they do not have gregarious caterpillars. The clumps of eggs laid by Small Tortoiseshells and Peacocks may be far easier for the parasites to find. However, this does not explain increased Red Admiral numbers - it's not as if nettles are scarce enough for a lack of consumption by one species to give an advantage to another.

Sorry, thinking out loud here, no science involved!

Dave

Are Painted Ladies and Red Admirals flying south in order to remain active? I daresay once butterflies reach southern Spain and north Africa there's sufficient warmth to fly throughout the winter not to mention reliable nectar sources.

If Red Admirals are flying south simply to go into semi-hibernation like they do in Britain then I don't really understand the logic, since winters on the continent can often be far more austere than those here in the UK. They may as well stay put.

David M wrote:If Red Admirals are flying south simply to go into semi-hibernation like they do in Britain then I don't really understand the logic, since winters on the continent can often be far more austere than those here in the UK. They may as well stay put.

But significantly shorter... Short and hard may well be preferable to long and mild, especially if you are a species that cannot enter a true hibernative state and have to rely on cold to induce torpor.

Guy

padfield wrote:

David M wrote:If Red Admirals are flying south simply to go into semi-hibernation like they do in Britain then I don't really understand the logic, since winters on the continent can often be far more austere than those here in the UK. They may as well stay put.

But significantly shorter... Short and hard may well be preferable to long and mild, especially if you are a species that cannot enter a true hibernative state and have to rely on cold to induce torpor.

Guy

I see, and I suppose any breaks in the cold winter weather are more likely to be warmer than those in Britain?

When I was living in Toulouse, we had short bursts of very cold weather punctuated by the odd day here and there when it was in the sixties.

Mating & Migration
It was assumed (by me), that female Red Admiral Imagines (adult butterflies) mate, generally before they migrate, to disperse eggs far and wide, helping to make them an evolutionary success. That might have been one reason why not very many were seen mating in the UK, as most were immigrants. In more recent years, for example, 2017 in the United Kingdom, it might have been seen that there were more homegrown virgin females, for males to fight over. As mating pairs were so infrequently seen in the wild in the UK, it might have been assumed, that females just mated once in their life time.
Factors that can affect migration after mating include temperature and local imago population density.
Heating up a mated female Red Admiral imago (Adult Butterfly), then harassing her (by many male imagines looking for unmated females) might equal quick dispersal as seen with some other butterfly species.
"A nuptial gift" (potential extra energy given while mating) might also be a reason for migration (female imago dispersal).
I hope that makes more sense for some enthusiasts.

Reference for: "Imagines" (Plural of Imago) definition:
Page 2, Life Cycles of British and Irish Butterflies, Peter Eeles

The New Naturalist "Insect Migration" NN No36 although writted many years ago gives details of butterfy movements North and South sometimes only a few days appart, at the turn of the season. The migration species chart on page 151 is still valid today, it gives species that often migrate here in the same years, and others that are negative with them so if its a good year for one you will not see the other.

There are tables in the back with yearly Migration numbers for the UK from 1850 to 1962.