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Photo#208319
Sand burrowing bee, wasp, or fly - Bembix

Sand burrowing bee, wasp, or fly - Bembix
Sunnyvale, Santa Clara County, California, USA
July 29, 2008
Size: around 20mm
Most of these are whitish, but some have yellow as the color that alternates with black in their markings. If they are flies they are doing a good job posing as a yellow jacket. They were observed in a large sandbox where they appear to burrow tunnels, and fly around patrolling and hunting. I was surprised to find that a number of paper wasps, Polistes dominula, were seeming to be attacking these wasps, or whatever they are. These Yellow (white) Jackets, by the way, are slightly larger than the paper wasps, but seemed to get the worse of it in the skirmishes. Also surprising: My niece was stung by one of the paper wasps. That's the first time I've seen anyone stinged by one! There were also some other interesting Hymenopterans in the vicinity. More on them later...

 
Indeed!
Large green eyes!

Also in Northern Cal
I saw a couple of these digging in slightly damp soil up here in Sacramento. Whatever it is, it's a bee with an agenda!

Bembix
it looks like this genus.

 
Bembix looks right to me...
...ID seems to be confirmed. These don't seem to exhibit the so called "wasp waist" but wasps they are. These guys can dig very fast! I wonder if they were burying their prey in order to keep them safe for their offspring to eat!

Colours
I unlinked the pictures because they are not the same individual. The colour differences can be due to them being different species or different sexes of the same species (in some species females are more whitish than males). Polistes attacks: Were the paper wasps trying to steal prey from the sand wasps? That would be an interesting behavior.

 
Mathias, That could be right!
I guess unlinking the pictures is the right thing to do, sorry you had to do it, I will do them separately from now on.

I might go ahead and link some of them together, though as individuals. For instance, I guess you noticed the prey that was being carried in one of the pictures? If not, take a look:


The prey is that black thing projecting from underneith of this wasp in the thumbnail.



I'm very curious what kind of thing the prey is! It is very large, and it may well be that the Polistes were trying to get them. I wondered what was going on, because it did not seem like a battle, yet there would constantly be just a few Polistes around the perimeter, a short fence, that was alongside the sand area where the sand wasps were located. It becomes easier to understand why my niece was stung when she had not be doing anything that should have aroused them. By being loud and fast moving, she was potentially driving away wasps that were bringing food to them. They ignored me because I was quiet. I don't know if that is an accurate explanation, but it does make a good "the moral of the story lesson" for her!

Also, interesting if the color difference are do to the sex of the wasps. It seems that the white ones are a much higher percentage of the ones that can be seen coming and going.

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