Butterflies and weather

[Michael Gochfeld]

Ron wrote: 

"Today's weather has very little to do with most of the butterflies we 
see today. The numbers being seen are because of yesterdays weather - 
actually last years (seasons). The cold winter and conducive conditions 
for egg and pupal survival. Before that conducive conditions for larval 
survival. Don't be surprised if the explosion in this years Vanessa 
species results in larval overcrowding, insufficient host availability 
for the size of the demand, increased disease and predation which would 
result in a bust year next season and the next and next. There will be 
more parasitic wasps and flies now that will have the upper hand in the 
food chain for a few years. Then the cycle will begin over again."

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This seems right on the mark.  Vanessa virginiensis (American Lady) was 
unusually common this spring (not in huge numbers, but commoner than 
most years), and a number of clones of Plantain-leafed Pussytoes, its 
commonest host in our area (Somerset Co, NJ) have been wiped out. It 
seems like the females almost prefer to lay in clones (about 1 m in 
diameter) that have already received eggs, even when there are untouched 
clones of plant nearby (within 10 m). We thought it might have to do 
with shade or sun, but no consistent pattern emerges. 

Fly parasites do seem to be common, but not enough data (yet) to 
indicate whether they are more or less common this year than previously.

However, on weeks where there is a lot of butterfly nectaring activity, 
there is a clear suppression of activity on really hot, bright 
afternoons (temp > 90f, strong insolation). 

Mike Gochfeld

 
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