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Hello,
I was watching a Sceliphron caementarium building its nest, and a fly arrived and watched it with me:).
It staid in the air, landed on my finger or on the wall just above the nest, but always facing the Sceliphron.
Is there a relationship between them or is it just fortuitous?

The fly (the little white thing in the corner:()in stationary flight, facing the Sceliphron:


The fly on the wall, watching the nest from above:

Southern France; 28 VII 2009

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THis seems to be a Miltogramminae fly (Sarcophagidae). Most likely it is a parasite of the wasp laying eggs into its chambers and outcompeting the wasp larvae.

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Thanks Gabor :)
I still wonder how a fly manages to get out of the layers of dried and hard mud.