I just learned that the wasp nest pictured is a mud dauber.
This is the second such nest I have on two edges of the same outside wall on adjacent years. I'm either inattentive, or they are particularly fast: the nest is built before I notice. One idea that worked with the first one was to spray shaving foam over it. Luckily the foam stayed there long enough, and the entrance was no longer menacing. The second one, pictured, seems to have served its function and is now empty.
The wikipedia page linked above suggests they might reuse a previous nest, and so I'll pull this off soon to avoid a recurrence.
Apparently they find something particularly attractive at this location. The color of the bricks? That the spot is shielded from rain? Is there a way to dissuade them from building in this particular spot?
I have also had yet another wasp nest below a layer of leaves in a bag near this entrance. Is this the same species? Might the presence of leaves act as an incentive to build the "organ pipe" mud dauber?
Best Answer
They build their nests in the late-summer to fall and I've found the best approach is to remove the nests as they build them. You'll hear the characteristic high-pitched buzzing as they deposit the mud. Scrape the nest off the wall or spray it off with your hose.
Mud daubers are not very aggressive, they can sting but usually don't and they don't swarm like hornets do. Their nests make a real mess, however. I have never noticed them reusing the same nest although they may build more mud tubes adjacent to old ones.
They tend to like shady spots like you have there on your porch. The nest is filled with spiders that are paralyzed by the venom and are used to feed the youngsters when they hatch.