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A scientific question for you to contemplate...

As there doesn't appear to be any noticeable Southerly migration back towards their original homeland in late summer, what is the evolutionary benefit which encourages these insects to fly so far? I appreciate that there will be more foodplant away from their original sites, but this is only a short-term fix as far as the Painted Lady is concerned. It doesn't help them survive from year to year. Surely if none ever get back "home" to breed and continue the species (and all the offspring die off in the cooler weather), the propensity for the "wanderlust gene" (if I can call it that) to be passed on through multiple generations should be lost. They obviously expend an awful lot of energy during their migration and there must be a benefit to the species or they wouldn't do it - (there is always an advantage of some kind to the evolutionary process), but apart from seeing a bit more of the world I find it hard to identify any in this case.


What does anyone else think?

Trev

A scientific question for you to contemplate... As there doesn't appear to be any noticeable Southerly migration back towards their original homeland in late summer, what is the evolutionary benefit which encourages these insects to fly so far?

I have been thinking about this! I am not a scientist but this is my theory:

The strategy the painted ladies are following must be successful because it is one of the most widespread butterfly species. What is happening is not really a migration - as it seems to be a one way journey! It is obviously a reaction to something happening in its home territory. If there are a lot of butterflies being produced in their home territory, if they stayed at home their offspring would eat all of their food plants, so they move. They move fast and into new areas and then breed there. If the area is good then they will have colonised, if not they will die away. One day, presumably, the UK will be warm enough for them - although currently any butterfly heading this way is probably going to be in for a shock through lack of flowers, pesticides etc..

Anyway, thats a layman's view! Treat me gently!

You may only be a "layman" , but you think like a scientist. You may have hit the nail on the head. Obviously they are pushing the boundaries to see how far they can get - "Dying trying" is better than just dying I suppose!

Any other thoughts?

Trev

It is so.

Watching The Incredible Human Journey on BBC 2 these last few weeks I was reminded how dramatically the climate in the Mediterranean/Middle Eastern regions has swung in recent geological history. Most species respond to climate change by creeping north and south (and up and down mountains) at the limits of their range, which is fine so long as there is appropriate habitat along the way. One of the great problems facing butterflies today, as the climate continues to swing, is that appropriate habitat is now so widely separated by urban areas, prairie farmland, roads &c. that this kind of 'following the climate line' is probably impossible for many without assistance. The painted lady, however, doesn't need to worry. It can leap from lattitude to lattitude without bothering whether there is a thistle bank in between!!

An interesting consequence of their not returing to their residency areas is that the selection pressures in northern Europe have no effect on the gene pool. Although the species is found all over Europe it is adapted to winter conditions only in North Africa. The colour of the underside is not dark, like our native hibernating Nymphalids, but pale, for more desert surroundings. It doesn't really have a diapause. In a sense, its massive capacity for dispersal limits its need to adapt to changing conditions. So long as the conditions it favours exist, it will find them.

As you say too, emigration as a means of population control has advantages too, which come into play even during climatically stable times.

Guy

Perhaps Guy if you could catch a stong Painted Lady and put a little camera on it and then you can record all the places it goes to and its destination Then we'd all know, 'The secret journey of the Painted Lady'
Shirley

That's a very good point, Shirley!! Or miniature GPS for painted ladies! More realistically, probably, I could have caught several hundred and marked them with a colour code on one wing. Then anybody who found one of these would know they had passed through Guy Padfield's place in Huémoz. I wonder if marking experiments have been done during this invasion.

Guy

Is it too late, maybe you could give it a try and we could do the same. The blue spot for 2009. I only saw one to-day
Shirley

I have not saw any today yet. My dad saw loads though, guessing they are going to places that they can breed in as where I have saw them here its not a good place for them to breed, but where my dad saw them is.

saw 12 or more today again, deffo year of painted lady, only whites and them seen, oh and a tatty holly blue

Trev Sawyer wrote:You may only be a "layman" , but you think like a scientist. You may have hit the nail on the head. Obviously they are pushing the boundaries to see how far they can get - "Dying trying" is better than just dying I suppose!

Any other thoughts?

Trev

Was discussing this with a colleague today and thought the same thing. The migration is a slightly more sophisticated version of a sycamore seed, the main point being to disperse the organism to new areas. The area underneath an adult sycamore won't support new seedlings because they are outcompeted for resources by both the adult and by other plants better adapted for lower light, scarce water etc. The wings on a sycamore seed have the potential to transport it to a new uncolonised patch of soil where its chance of germinating, surviving and reaching maturity are all better.

The reason I say that the PL migration is more sophisticated is because it doesn't happen every year. What I wonder about is whether there is some density dependent trigger to the PL migration, with migration only happening in years where exceptionally high numbers of adults emerge. Or is it that the migration always happens but is far less noticeable because of the relatively low numbers in normal years.

Does anyone know where migrating PL mate and lay eggs?

Bill

They migrate every year - I've seen them every year since I was a kid. Some years they are relatively scarce (2005 was a recent bad year) but in a normal year they are a common butterfly in most of Europe from mid-end May, their numbers increasing during the summer as they breed. They usually arrive as masses, rather than as individuals, so the first sighting of the year is generally of several and most years there is a day where you can say, 'the painted ladies have arrived'. This is probably more marked here in Switzerland than in England because even the relatively short span of the channel is an obstacle (painted ladies are much commoner in Brittany in a normal summer than in Britain).

Guy

padfield wrote:They migrate every year - I've seen them every year since I was a kid. Some years they are relatively scarce (2005 was a recent bad year) but in a normal year they are a common butterfly in most of Europe from mid-end May, their numbers increasing during the summer as they breed. They usually arrive as masses, rather than as individuals, so the first sighting of the year is generally of several and most years there is a day where you can say, 'the painted ladies have arrived'. This is probably more marked here in Switzerland than in England because even the relatively short span of the channel is an obstacle (painted ladies are much commoner in Brittany in a normal summer than in Britain).

Guy

Thanks Guy, what about crossing the Med. Is that not a bigger barrier than the channel?

Bill

I know from personal experience that a lot come over at Gibraltar, where the sea crossing is very narrow. But I'm sure they cross elsewhere too when the winds are favourable.

I mentioned Brittany because that was where I often went on holday with my parents when I was a teenager, and afterwards when I was a student. It struck me that there were always more painted ladies there than back home in the UK.

Guy

Very variable in UK compared to the continent - and considering that it is only 20 miles from France it seems that population density also governs how far they fly...?
Couldn't resist one more...
early morning top-up...

Apparently there is going to be a piece about the migration on BBC Springwatch, Wednesday - BBC2. Programme starts at 8pm.

CW

padfield wrote:I know from personal experience that a lot come over at Gibraltar, where the sea crossing is very narrow. But I'm sure they cross elsewhere too when the winds are favourable.

I mentioned Brittany because that was where I often went on holday with my parents when I was a teenager, and afterwards when I was a student. It struck me that there were always more painted ladies there than back home in the UK.

Guy

I was in Antibes at the start of May, and there were dead Painted Ladies being washed up on the beach.

It did look like some had made it across the sea though. This one photographed below was nectaring on cliff-side vegetation, quite possibly having just made it ashore.
There was a report in the French press last year of a Painted Lady making it to one of the Southern Ocean islands - Kerguelen I think - over 2000 miles from the nearest major landmass.

Thanks for being gentle!

I took the day off last Friday and spent an amazing day in Ashdown Forest with PLs rushing past every minute or so. It was incredible to see that 95% of them followed precisely parallel flight paths - approximately due North. Almost like drawing a series of grid lines across the landscape. Every so often, though, one would fly across at right angles! What really struck me was how powerful and purposeful their flight is. I know I shouldn't anthropromorphise (!) but it is somehow sad to think that most of these wonderful creatures were heading at full speed on a one way journey!

Here's a link to the piece on BBC Springwatch about the Painted Ladies.

http://www.youtube.com/watch?v=67okr6O229Y

To be honest, I was a bit disappointed (not sure what I was expecting, though - perhaps an interview with someone who actually knows what they're talking about?)

CW

walpolec wrote:Here's a link to the piece on BBC Springwatch about the Painted Ladies.

http://www.youtube.com/watch?v=67okr6O229Y

To be honest, I was a bit disappointed (not sure what I was expecting, though - perhaps an interview with someone who actually knows what they're talking about?)

CW

idk, I was expecting a little more, but the shots of one laying eggs was pretty good to see and it did explain why the butterflies leave Africa (I never actually knew before)

Yes - "Don't worry, Springwatch will solve the mystery of reverse migration in Painted Ladies for Butterfly Conservation"
We can all rest easy in the knowledge that it is in the safe hands of Kate Humble!
H'mmmmmm