Message From Mary Beth Prondzinksi

Royce J Bitzer mariposa at
Mon Oct 6 14:03:47 EDT 2003

At 11:01 AM 10/6/2003 -0500, Robert Dana wrote:
>Regarding Mary Beth's report of the appearance of large numbers of V.
>cardui in Chicago on Sept. 18:
>Here in Minneapolis the irruption began about Sept. 10. We had a
>protracted summer drought here with warmer than average temperatures.
>Our first heavy rainfall in a number of weeks occurred the evening of
>the 11th continuing into the 12th. There has been some speculation that
>the emergence was triggered by the rain, with the large numbers being
>the result of an accumulated pool of aestivating pupae. I am sceptical
>of this hypothesis, but maybe others reading this can offer some
>support. Even after several nights of freezing temps here there are
>still butterflies around, nectaring or basking. I have seen no courtship
>behavior or mating pairs. When the butterflies first appeared I noted a
>behavior I hadn't ever seen in Vanessa before: individuals soaring with
>horizontally fixed wings, riding small thermals upwards until I couldn't
>see them any more.

I also have doubts about the eclosion-triggered-by-rainfall hypothesis, 
since it was similarly dry in August in central Iowa, and yet there were 
large numbers of V. cardui building up through mid-July through 
August.  From reports I've received so far, I suspect that the butterflies 
might have moved northward into your area from a source region extending 
from central Nebraska through east-central Iowa and possibly through 
central Illinois and southwest Indiana, where they had been abundant as far 
back as mid-July.  They also seem to have had moved southward into 
Lawrence, Kansas beginning the first few days of September.

There were several days in mid-September, when I was recording flight 
directions and other behavior, that I saw the butterflies rising and 
circling and riding thermals upwards, much in the same way as Monarchs 
often do.

>I used to have the URL of a web site that took reports of Vanessa
>observations and compiled them on a map--but I have lost it. Can anyone
>provide this?

I suspect the web site that you're referring to is mine (address listed 
below).  I've been mapping locations where "large numbers" of Painted 
Ladies have been observed during the current outbreak, and will be updating 
the map soon with additional observations.

>Robert Dana, Ph.D.
>Natural Heritage and Nongame Research Program
>500 Lafayette Rd, Box 25
>St. Paul, MN 55155
>651 297-2367
>Email: robert.dana at


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