#mud dauber

Blue Mud Daubers - SOCAL, USA:

So, after speaking to this friend off line, we know that this species lives SoCal, and the species is likely...

Common Blue Mud Dauber (Chalybion californicum), family Sphecidae, live over much of the US, Mexico, and far southern Canada

In low light this wasp may look blackish, but in full light looks iridescent blue.

Females sting, but males cannot.

They have been introduced into the Caribbean, Hawaii, and parts of Europe.

Females either construct their own mud nests, or refurbish the nests of other mud daubers (even of other species).

Adults feed on nectar.

Females sting and paralyze spiders (mostly black widows). They place the spiders in the mud nest, and lay an egg on them. The larvae feed on the spider after hatching from the egg.

They hunt prey on low vegetation, on the ground, and under rocks and logs.

photograph by Nell Cant & Bob Noble

Chicago, IL, USA - photo by Carol Blaney

photograph by Bug Eric

Now another possibility is this one as well...

Steel Blue Cricket Hunter (Chlorion aerarium), family Sphecidae, found across the US, far northern Mexico, and extreme southern Canada.

Adults feed on nectar.

Not found near homes that often, they tend to frequent open fields.

Females paralyze crickets. They dig burrows into the ground, where the place the cricket. They then lay an egg on the cricket, which the larvae feed on.

this mud dauber wasp (Sceliphron caementarium) seemed distressed about something in her clay nest. Turns out it had been commandeered by a keyhole wasp (Pachodynerus nasidens), who was now aggressively asserting ownership

keyhole wasps, which hunt weevils and other small beetles, will opportunistically nest in any sort of small cavity (such as a keyhole). The existing literature on this species doesn’t say anything about taking over other wasp‘s nests, only that they sometimes refurbish abandoned nests, but I guess this one didn’t get the memo.

This isn't the worst of their mischief though- they also have a habit of building nests that clog up the airspeed measuring instruments in planes and have caused several fatal crashes.