Vanessa at night - migrations

[Eddie John]

And I'm grateful for your kind remarks, Kenn.  Yes, I did say it would be my final contribution but if anyone with a serious interest would like to contact me direct, please do so.  (That's not meant to sound conceited, by the way!)

May I leave the subject with this wonderfully descriptive account, quoted by several people since (including me, in the Ent Rec paper)......... 
"A delightful account of an observation by S. B. J. Skertchly, quoted by C. B. Williams in The Migration of Butterflies, but reproduced here from Barrett & Burns (1966), beautifully describes a scene in the Sudan: ‘From my camel I noticed that the whole mass of the grass seemed violently agitated, although there was no wind. On dismounting I found that the motion was caused by the contortions of pupae of P. cardui, which were so numerous that almost every blade of grass seemed to bear one. Presently the pupae commenced to burst. Myriads of butterflies sprinkled the ground, and when the sun shone, dried their limp wings. About half an hour after the birth of the first, the whole swarm rose as a dense cloud and flew eastward towards the sea".

Don't, anyone, dare ask how many cardui can cling to a swimming camel!

Eddie 

    -----Original Message-----
    From: Kenn Kaufman <kennk at ix.netcom.com>
    To: leps-l at lists.yale.edu <leps-l at lists.yale.edu>
    Cc: Eddie John <eddie at grayling.dircon.co.uk>; Nick Greatorex-Davies <ngd at ceh.ac.uk>
    Date: 05 February 2002 06:25
    Subject: Re: Vanessa at night - migrations
    
    
    Eddie John wrote:
    
    >This will be my last contribution on the subject,
    >otherwise I can anticipate being asked whether
    >a cruise ship from Israel docked in Cyprus at
    >the same time! ...
    
    I for one am grateful to Eddie John, Nick Greatorex-Davies, and others
    for their detailed posts about observations of butterfly dispersal from
    the Mediterranean region, the U.K., and northern Europe.  And I'm sorry
    that those posts were met with badgering  from The Man Who Always
    Contradicts People (old Python reference there).  Despite how it might
    appear, many of us Yanks are actually sane and open-minded, and quite
    interested in such relevant information.
    
    The significant question here involves butterflies (such as Vanessa) in
    strong dispersal mode that find themselves over open water at nightfall.
    Do they keep going?  Some believe (well, okay, one person believes) that
    they must fold up and drop into the drink within an hour after dark.
    That's not impossible, given that some episodes of butterfly dispersal
    are suicide flights for all practical purposes.  But in areas such as the
    Mediterranean, where a crossing is feasible, there would be very obvious
    selective advantages to continuing to fly.   Those that fold in the dark
    and drown are certainly not going to pass along any genes, while those
    that continue flying in the dark just might make it to another landfall
    where they could breed.  It seems quite plausible to me that this kind of
    selective pressure over a few thousand generations could enhance the
    tendency of determined dispersers to keep flying when there's no safe
    place to land.
    
    Of course, this has nothing to do with a lack of butterflies cavorting
    about the buddleias in the moonlight.  It also has nothing to do with V.
    cardui migrating through the southwestern U.S. -- if they're flying over
    land, it's no surprise if they stop for the night.  But it does have
    significance for questions of biogeography.
    
    Given that we're talking about an unusual set of natural circumstances
    (strongly dispersing individuals in free flight over open water), I don't
    see any way to approach this experimentally.  We can't just put
    butterflies in a flight cage overnight and expect them to behave in the
    same way.  Good old observation in the wild seems the only likely way to
    make progress on the question.  Lepidopterists who are fortunate enough
    to witness such an event would do well to document as many details as
    possible and to publish those observations.  The geography of North
    America is not well suited to such observation, as we don't have many
    huge bodies of water at the right latitudes, so I'll continue to
    appreciate such reports from our friends on the other side of the
    Atlantic.
    
    Kenn Kaufman
    Tucson, AZ
    
    

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