End-of-season observations

[Runar Krogen]

Hello 

The winter has entered Trondheim. We have experienced several frosty nights
since mid-September. The first snow fell on October 16. above 200 meters,
later on even down to sea level. Now the snow has melted below 500 meters
and at this moment it is mild, 10 centidegrees.

The last native butterfly, one Polygonia c-album, was observed in my garden
on September 27.

But some strange strugglers have been fighting against the conditions. On
October 11. I observed the last Vanessa atalanta. The same day I found a
pupae of this species. Still there is a chance that some may be alive here
around. 

But what in my opinion is really strange is the discovery of 2 Vanessa
cardui larvae, both alive. This was yesterday, October 24!!! I found them
on thistle (Cirsium helenoides), and when I brought them inside my house
they became active and began to eat. The caterpillars, one 4. instar and
one early 5. instar, have survived frost, snow, sleet, rain and strong
winds, coniditions I do not combine with Vanessa cardui. I must mention
that on October 10., I found 25 cardui larvae and eight of those were dead.
Some were only 3. instar. 

All the caterpillars originate from a migration of Vanessa cardui that took
place late June/early July. Also Vanessa atalanta migrated to this region
during the same time. The caterpillars are delayed because of the
conditions up here (63.5 degrees north).
The same phenomenon took as a matter of fact place in 1996 here around. An
experiment with pupaes of Vanessa atalanta that year showed that one
survived 2 months outside even when being exposed to temperatures down to 5
centidegrees below zero for shorter times.

Anyone who have any "winter experiences" with the vanessas? Surely they do
definitely not survive the winter up here! Their occurance is based upon
migration.

Runar Krogen, 
Trondheim, Norway
rkrogen at online.no