[Syrphidae] freeze tolerance in tree-hole species

[Frank Van de Meutter]

Hi all,

I planned this winter to start a search for some rare water filled 
treehole/treecavities inhabiting syrphids in Belgium. Winter is however 
particularly harsh here (and over much of Europe), and all these small 
water bodies that I visited are frozen for more than six weeks now. It 
appears to me that the whole of the water content in the tree rotholes 
and cavities is now frozen. This makes me question whether syrphid 
larvae will be able to survive these conditions? Even if not all is 
frozen, they should experience oxygen shortage? Comparably, in ponds and 
pools, it is known that severe frost may also wipe out a considerable 
fraction of the aquatic community (though I know nothing on syrphids 
living there). When the water starts to melt I will see whether many 
dead larvae can be found. Right now, I would like to ask whether anyone 
has some previous experience/knowledge on this?


beste wishes,

Frank