Nymphalis-species

[Jaakko B Kullberg]

In Finland spp. antiopa, io, urticae  and c-album are common and
overwinter succesfully year to year. Spp. polychloros, wau-album & 
xanthomelas are more irregular and extremely rare. Two latter have
become more rare after the beginning 70's. io is a newcomer occurring
only in the S-Finland. 

We have many times wondered here why xanthomelas and wau-album stay away
from our territory. Definately the reason can not be cold winters as in
the most of Russia you can expect temperatures 40 degrees below zero.
I have visited several times in places where these two and also antiopa
occurs in numbers. I think that the case of these three species is quite
similar. 

Last spring I visited in Buryatia (east of Lake Baikal). All three
species were quite common, but only locally abundant. They occurred in
great numbers only in places which are cold at night eg. moist lowlands
with a lot of snow, boggy places etc. These places are often
very hot at day and butterflies visited commonly on birch trunks to suck
sap. In my mind antiopa & xanthomelas were more abundant in Betula
forests and xanthomelas in Salix groving places. Eg. in one place we
found a true mass occurrence of wau-album where there were old pupae in
every tree trunk. There were also about 1000 specimens overwintering in 
our cottage! 

Well, what Siberia has and we do not? There is more continental and in a
way more expectable climate - sunny summer and cold winter. However this
is basically quite the same we have too in Finland. Our summer is not
limiting for the species as even atalanta and cardui can make brood here
and antiopa is in the flight in early August - every year. At winter you
can expect almost anything here in any single week during winter.
Atlantic warm winds come often and temperature comes up. Or then
Siberian cold comes and there -25C in the very next day. However most of
you know that overwintering Nymphalids choose cold places to overwinter
- to avoid too warm temperatures. 

Then we have two seasons left: autumn and spring, Autumn is not a
problem - clearly - as most specimen disappear already in early
September. But at spring there can be difficulties. 

In Siberia spring
comes relatively late especially those places where xanthomelas etc. are
abundant. At daytime it may be warm, but every night there is severe
frost eg. -5 to -15C in Barguzin valley W of Baikal (in the beginning of
May). However in May whether is very sunny and there rarely rains there
and forest fire are problematic. I think (not know) that cold winters
give a tip for the butterflies - don't lay eggs yet = too early. And
then warm and sunny days make sure that small caterpillars grow quickly
the first and most vulnerable instars. 

Well, in Finland spring comes and goes several times without really
starting. Snow cover often melts because of rains - not sun. Butterflies
which though that spring is here in early April may have to wait month
the next chance to get flight again. Extremely bad is if they have
managed to lay eggs too early. I think that the most contrastic
difference to Siberia is the spring time. In a way when summer/spring starts
in Siberia it is more continuated progress than in N-Europe, where more
often are season obscuring weather situations. Also remember that in
spring the amount of solar radiation is greatest. 

Eg. few years ago one
spring almost wiped out A. urticae from Finland! Sunny early spring
waked up them and then came cold and rainy weather which continued to
late June. It must have been ruff for both butterflies anf caterpillars.
The latter were of course longer time vulnerable for predators and disease
- and when the summer finally came all the plants were long ahead of the
defoliating insects =the quality of food were sinking already. 

In general I would like to point the importance of solar radiation to
young caterpillars. Too often we see publications where mean temperature
is used in studying flight periods etc... Insects rarely live as
caterpillars in 2 meters hight in mid air, from where we got the
daily temperature results. I counted soil temperatures when studying
grasshoppers in sand dune area in SW-Finland. It was amazing how
quickly sand get warm and how deep it's effect went. In sunny weather
the sand was more than 70C in few hours in 2 cm depth and around 40C in
5 cm. I wonder that it is best to escape deeper in the sand to avoid
coagulating of proteins.  

Well, to the point, I suggest that our spring is not good enough for the
butterflies - they don't / can not wait enough long time before they lay
their eggs. And therefore caterpillars suffer of cold and cloudy
weather. 

jaska
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Jaakko Kullberg, M. Sc. (Biology)
Collection Manager
Finnish Museum of Natural History
Division of Entomology, P.O.Box 17
FIN-00014 University of Helsinki
Phone: 358-9-191 7425
FAX:   358-9-191 7443
e-mail: jaakko.kullberg at helsinki.fi
        jkullber at cc.helsinki.fi
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