January 2013

[Neil Hulme]

Hi David,
Yes, these will be from a later generation of butterflies hatched to the south. We also now know that some migrations occur at significant altitude, taking advantage of more suitable airflow directions and reverse thermoclines.
Neil

[Neil Hulme]

Hi Guy,
Great footage. We have lift-off!
Neil

[Jack Harrison]

wouldn't the insect 'feel' colder if there was a 20kph easterly breeze constantly buffeting it?

No, it wouldn't. It might find the gusty winds annoying. It would find navigating difficult. But birds do it, bees do it, even educated butterflies (might) do it.

See this example.

vector triangle.jpg (15.91 KiB) Viewed 675 times

Jack

[David M]

wouldn't the insect 'feel' colder if there was a 20kph easterly breeze constantly buffeting it?

No, it wouldn't. It might find the gusty winds annoying. It would find navigating difficult. But birds do it, bees do it, even educated butterflies (might) do it.

I'm happy with the directional stuff, Jack, that stands to reason, but how is it that I feel colder on a 9c December day with 20kph winds blowing than I do with a 2kph wind blowing when a Painted Lady would not?

[David M]

Hi David,
Yes, these will be from a later generation of butterflies hatched to the south. We also now know that some migrations occur at significant altitude, taking advantage of more suitable airflow directions and reverse thermoclines.
Neil

Thanks for this, Neil. I must confess I hadn't even entertained the prospect of butterflies migrating over the English Channel in deepest winter (irrespective of altitude).

What puzzles me now is how nature can support something that seems so counter-intuitive. Surely, these insects must be at their limit even during the most benign periods in winter. There appears to be one almighty risk for seemingly no tangible benefit.

[Padfield]

I'm happy with the directional stuff, Jack, that stands to reason, but how is it that I feel colder on a 9c December day with 20kph winds blowing than I do with a 2kph wind blowing when a Painted Lady would not?

There are two reasons for this. One is that wind chill is caused by moisture evaporating on the surface of the body - and your body is more moist than that of a butterfly. A dry sensor does not record wind chill. The other is that, as Jack says, the relevant wind speed is that of the air relative to you, not the air relative to the ground. When you stand in a 20 km/h wind it moves at 20 km/h relative to you. But if you leapt into the air and floated with the wind it would be stationary with respect to you, just as no water flows past you if you float down a raging stream. When a butterfly flies, any wind chill it experiences will be caused by its own motion through the air mass, not the motion of the air mass with respect to the ground.

Guy

Oh - and butterfly bodies are much hairier than yours, further minimising the relative movement of air close to the surface.

[David M]

There are two reasons for this. One is that wind chill is caused by moisture evaporating on the surface of the body - and your body is more moist than that of a butterfly. A dry sensor does not record wind chill. The other is that, as Jack says, the relevant wind speed is that of the air relative to you, not the air relative to the ground. When you stand in a 20 km/h wind it moves at 20 km/h relative to you. But if you leapt into the air and floated with the wind it would be stationary with respect to you, just as no water flows past you if you float down a raging stream. When a butterfly flies, any wind chill it experiences will be caused by its own motion through the air mass, not the motion of the air mass with respect to the ground.

Superbly succinct as ever, Guy. Thanks for this. I'm getting a different sense of perspective on it now though I still struggle to imagine a butterfly crossing the Channel in December.

[MikeOxon]

wind chill is caused by moisture evaporating on the surface of the body

Certainly, a creature that relies on an evaporative cooling system (like ourselves) will experience a strong wind-chill effect but any creature that attempts to maintain a raised body temperature will suffer a more rapid loss of heat in moving air than in still air.

This 'forced cooling' effect is because air is a good thermal insulator and still air can, therefore, provide an insulating blanket. Many butterflies have a dense body covering of fine hairs, which trap an insulating layer of air close to the body surface. A strong air-flow can disrupt this blanket and lead to more rapid cooling of the body. Of course, butterflies are not warm-blooded, in the same sense that we are, but they do generate heat, especially in their flight muscles, which allows them to function in low air temperatures.

Mike

[Neil Hulme]

Hi David,
I just found an interesting passage in ‘The Butterflies of Britain & Ireland’; Jeremy Thomas writes “They (Painted Ladies) arrive as early as January or February in some years, when regular sightings are made all along the south coast”.
Neil

[Jack Harrison]

Neil had some very valuable ideas but he is just Mister Hulme. Jeremy Thomas is a PROFESSOR so I pay far more attention to what the Professor says.

In truth Neil, you worked it out without any pre knowledge what Jeremy had deduced. So - serious hat on now - why don't you go for a Doctorate on his Imperial Highness and then later, a Professorship for studying the Duke? Yes I am being serious. You can do it Neil. I volunteer to proof-read - what an easy job that would be! (but my name would appear on the treatise!)

Go for it.

Jack

[Neil Hulme]

Thanks Jack, but I've already spent plenty of time at university, from what I remember ... and I don't think I'd have half the fun I did back then, from what I remember.
BWs, Neil

[David M]

Hi David,
I just found an interesting passage in ‘The Butterflies of Britain & Ireland’; Jeremy Thomas writes “They (Painted Ladies) arrive as early as January or February in some years, when regular sightings are made all along the south coast”.
Neil

How embarrassing. I actually have that book.

I'm still amazed that they can do this in the middle of winter, but then nature has a habit of confounding expectations, I suppose.

[Cotswold Cockney]

I have nothing learned to add, but can illustrate this pre-take-off warming up in a chequered skipper:

http://www.youtube.com/watch?v=j1RbYCEEAQs[/video]

The day had rather suddenly cooled when I took this.

Guy

I have always regarded skippers as 'half-moth' butterflies. Moths frequently do that muscle warming exercise prior to taking to the air.

So do larger butterflies. That massive Apaturine Oriental relative of our own Purple Emperor, the Great Purple Emperor ( Sasakia charonda ~ The National Butterfly of Japan ) and it's even larger relative in mainland China, the massive Sasakia funebris, have sometimes spent up to two minutes or more doing that whilst holding on tightly with their four legs to avoid premature take off. I am convinced it is to warm up key muscles. Something human athletes do to avoid stressing muscles or ligaments too. Those butterflies did that in large cages in my garden or greenhouse before the sun warmed things up.

I have also seen our own species of Purple Emperor do that too but it may have done so for reasons other than warming up as it was observed by me in mid afternoon on a warm day. These large butterflies exercise their wings through an angle of about 45 degrees of wing movement above and from the horizontal plane either side of their thorax whilst holding on tightly.

In a favourite Sussex wood, I once saw a male fly down a female at the end of their courtship flight routine and when both reached ground level, they faced each other head to head closely with the male vibrating its wings rapidly through that angle above the horizontal plane. A one in a million chance observation never since witnessed in the wild although the facing each other stance with the male vibrating its wings that way I did once witness in a large breeding cage.

This is S.funebris :~



Unusual for a "Purple Emperor" as the colouration mimics Black Swallowtails known to be poisonous and thus affords some protection from potential predators.

The closely related Great Purple Emperor of Japan Sasakia charonda in colouration follows the more normal Apaturine scheme of things with males having a rich purple-blue flush on their upper wing surfaces which the larger females lack :~



Feeding on a sap run :~



These large butterflies have approximately double the wing area of our species. Here's a picture of the nearly fully grown larva of S.funebris I had the pleasure of rearing several examples for a few generations on trees in my garden back in the 1980s. :~



Memories of great days ... Cannot sleep tonight. Dont know why. As I type this I glance out of the window into a freezing, windless and dark January night with an ever thickening fog and much frost. Right now, that first eagerly anticipated sighting of a butter coloured fly soon or come spring seems a remote possibility....

I once picked up a Death's Head Hawk Moth by the thorax between finger and thumb after it had spent several minutes warming up and hovering in its large flight cage trying to excite successfully a female. It was HOT to the touch, not merely warm but hot. By the way, be careful if you ever do this. These magnificent moths have a very sharp pin like process in that area of the thorax which can penetrate the skin easily if you are not careful or are unaware it was there as I discovered when first handling these moths in captivity.

So be careful when out and about when Death's Head are active ...

[Neil Hulme]

Hi CC,

As always, some fascinating recollections. I agree that your amorous male Emperor would have been vibrating his wings for a different reason, in front of the female which he had pursued onto the ground. He would have been fanning her with the great smell of Brut, in a futile attempt to woo her - she will already have been mated. I have only observed this behaviour at close quarters once myself, perhaps in the very same Sussex wood, although I've seen the preceding, tumbling drop a couple of times, with the female usually shooting off at very high speed just before they hit the deck, leaving the courting male somewhat bemused. This rejection behaviour was first described by that great servant of HIM, Ken Willmott. Such activity is almost always observed in the afternoon, as the peak time for mated females to be out egging is 1.00 pm - 3.30 pm (>90% of my female sightings occur within this window).

When the aerial pursuit of females is underway the quantity of pheromones in the air must be considerable. Twice I've observed the confusion that sometimes occurs when more than one male is a tailing a virgin. Mistaken identity can result, with over-excited males 'trying it on' with each other. An amorous male must never take his eye off the ball!

I've seen the successful conclusion to courtship pursuits on 4 or 5 occasions, and the coupling has always occurred high in the canopy, usually lasting for 3.5 hours or more (an average performance ). Sadly, this means that the act is seldom observed close-up in the wild. However, one lucky chap I know, Keith Capon, was once leaving Botany Bay after an unsuccessful search for grounded males (it was far too windy), when a pair in cop were blown from their perch and fell at his feet. How lucky is that!!!

Great image of Sasakia charonda . The Japanese have got it right - we should recognise iris as our national butterfly.

BWs, Neil

[Cotswold Cockney]

The Sussex Wood I frequently observed those iris courtship flights including the one with the male's fast vibrating wings was Minepit Copse in 1972. I had observed iris there from the 1960s. I also saw the same thing several times in a less well known part of the Bentley Woods complex and other Wiltshire Woods in the 1960s.

If you ever have the chance to handle a wild female iris it is easy to check if it has been fertilised. There is invariably a trace left of the male's spermataphore transfer slightly protruding from the female's Bursa Copulatrix. I could check for that minute trace as I had excellent eyesight back then. Now I would need to use a x10 hand lens.... I could and did spot the occasional ovum on the Sallows twenty foot up. On several occasions, I also found ova on the underside of the leaves. The fully laden female is relatively heavy and I have observed one alight on a leaf which would hang down. The sudden weight shift meant that the speedy process of egg laying sometimes results on the ovum being deposited on the under side of the leaf. Makes no difference to the little larva when it hatches which always has a silk safety line.

I last visited Minepit Copse about six years ago. Much has sadly changed.The small Douglas Firs planted back in the late 1960s were then largely overcrowded by many fine specimens of Broad Leaved Sallows which the females laid on profusely. They now look like this. Massive trees :~



That's my Rover 620ti in the pictures to illustrate the scale and shows just how large those Firs have grown now excluding much smaller shrub and plant growth.



Nothing lasts forever.

[MikeOxon]

Moths frequently do that muscle warming exercise prior to taking to the air.

Apparently Bumblebees can uncouple their flight muscles from their wings, so that they can warm up without taking off!

There's a video taken with a thermal-imaging camera, at http://www.bbc.co.uk/nature/life/Bumblebee#p003kmh2

Mike

[Cotswold Cockney]

Moths frequently do that muscle warming exercise prior to taking to the air.

Apparently Bumblebees can uncouple their flight muscles from their wings, so that they can warm up without taking off!

There's a video taken with a thermal-imaging camera, at http://www.bbc.co.uk/nature/life/Bumblebee#p003kmh2

Mike

That is very interesting Mike. Amazing even!

My immediate first thoughts are that the process would be rather like a very fit footballer powerfully miss-kicking the ball with an "air shot" and risk damaging ligaments and muscles with that excess of power going nowhere without an end product.

I wonder what Wolfgang und freund make of it :~

http://www.youtube.com/watch?feature=pl ... QyUKnCf0YY[/video]

Well.. bit of a giggle and helps to pass the time these far too long winter nights. Mind you, couple of clumps of Snowdrops showing locally ... it's a sign....

[marmari]

Three Painted Ladies at Wheelers Bay on the Isle of Wight today.
Pics on my Personal Diary soonish.

[nomad]

Getting back to the Painted Lady sightings. I am still finding it very hard to believe that this species would migrate northwards into a cold European winter from a very warm region. What would be the point in this, they would not be able to breed here. This species has been proven to return across the channel when numbers have been high before the onset of cold weather. I really find it very difficult to imagine that this species would fly such a great distance at that time of year let alone survive such a ordeal.

nomad

[MikeOxon]

that excess of power going nowhere without an end product.

...but the end product is the heat output, which enables it to fly and reach nectar sources ahead of its competitors!

Mike