Vanessa at night - migrations

[Stan Gorodenski]

Paul Cherubini wrote:
> 
> Yes, Ken some of us think Vanessa butterflies are likely functionally incapable
> of oriented flight within an hour after sunset because they lack dark
> adapted eyes - in plain english they are probably functionally blind at night
> 
> Page 228  R.F. Chapman - The Insects, Structure and Function:
> (College textbook used for Courses in Insect Morphology & Physiology):
> 
> "The flight activity of many insects is limited by light intensity and
> Lewis and Taylor (1965) conclude that this is the major factor
> controlling times of flight.  For instance many day-flying insects, such
> as butterflies and Hymenoptera, are not active in the dark and
> aphids will not take off when the intensity falls below 20 ft.-candles."
> 

However, as E.B. Ford states in his "Butterflies", 'Near objects, seen
by many facets, are probably very distinct, but they will be rapidly
blurred as they recede". In the context of mass migrations, I have to
wonder just how important eyesight is? Could simply being able to detect
the illumination from the moon be sufficient to orient the cloud? From
Orley Taylor's work on the magnetic effects on Monarch orientation, it
would appear that Monarchs could successfuly migrate at night, even if
they may be blind.
Stan

 
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