Sand Wasp? Really?

Earlier, I mentioned that I had witnessed what looked like two bees fighting.  Originally, I thought the attacker was a beewolf.  Beewolves are sphecid wasps that prey on bees (of course) in order to lay their eggs within the victim's body.  Well, it turns out that beewolves are way bigger than the bug that attacked my bee.  It took a while, but I think I've finally managed to identify it.

Bembix americana

Scientific Name: Bembix americana

Common Name:  Sand wasp

Color:  Black and white or yellow thorax,

Size: Roughly 1.5 centimeters in length

Social Type:  Solitary insect

It appears to be a sand wasp.  The female, as the name implies, digs short single chamber tunnels which are used to deposit their eggs.  They place insects that they've collected inside the tunnel to feed their young.

Sand wasp 'nest'

And they dig really, really fast.  A single wasp can dig a chamber in just a few seconds.  I found a great example of this on YouTube, which was created by LampoFilm

See?  I told you they're fast!

While classified as predators because they harvest insects to feed their larvae, the adults feed on nectar.  That's a pretty big lifestyle change, if I've ever heard of one!

And not only do they feed on nectar, but they're not aggressive. Unless you happen to be small with six legs, that is...

You've seen my photo, and you've watched LampoFilm's video.  You're probably wondering why I say that I think I've identified the insect in question, rather than that I'm sure.

Well, these wasps tend to prey on flies.  Now, forgive me for saying so, but I don't consider flies to be particularly tough creatures.  Their defenses are... well... do they even have any defenses?  I realize that a beetle was what was dragged into the tunnel in the video, rather than a fly, but I'm still having trouble wrapping my mind around the idea.  How could that tiny wasp take on a bee?

Maybe the bee was sick, or maybe the sand wasp is just that tough.  There must be some explanation that I can accept!