Blue Mud Dauber Wasp

2009 March 14

When I was a kid, I used to find these blobs of mud stuck on our farm buildings, mostly under the eaves or in other spots where they would be protected from the rain. When I broke them open from time to time, they were either filled with paralyzed spiders, or had a wasp pupa inside. I’d often watch them being repaired and stocked by wasps that looked like this:

This is another old picture that I took in 2007, and the wasp was large enough that I tried getting the pictures without the macro lens, which is why the pictures came out a bit blurry.

[Note added in 2014: I’ve since taken some better pictures of blue mud dauber wasps, if you want to see the details better. They are here.]

I also refrigerated it, which made it pretty much act as if it were dead until it warmed up again. This seems to be a trait of hymenoptera – ants, bees, wasps, and sawflies don’t seem to take cold temperatures very well.

Anyway, it is a Blue Mud Dauber, genus Chalybion. The metallic blue color is quite striking, and the elongated, very thin waist is very distinctive.

While they are wasps, and they can sting, they are solitary wasps and don’t generally sting people except in extreme self-defense[1]. They mainly save the stinging for the spiders that they catch to feed to their grubs. What they do is this: first, they find, refurbish, or build out of mud a tube about one-quarter of an inch in diameter (roughly 5 mm). Then, they go and find spiders that they ambush, and quickly sting just so. They don’t kill the spider outright, because then it will start to rot right away. Instead, they just paralyze it, which keeps it fresh[5]. Depending on how big the spiders are, she’ll nab five or six of them and stuff them into the tube. Then she’ll lay an egg on them, cap the tube off with more mud, and start stocking the next tube. The egg then hatches, and the grub eats the paralyzed spiders as it grows. Then, come around fall, it pupates and waits for spring, at which time it finishes, pops out of the nest, and flies off to do in some more spiders. It’s a lot of work to build new nest tubes out of mud, so frequently they’ll just clean out an existing old nest and start over. They often take over the abandoned nests of other kinds of mud daubers (particularly nests of the related Black and Yellow Mud Dauber), or sometimes just take advantage of tubular openings that they find[2].

Whether these wasps are good or bad to have around kind of depends on your opinion of spiders. I’ve read that they will actually prey on black widows, if that’s the sort of thing that concerns you. Around here, though, the spiders they eat are really the sorts of things I’d rather keep around. Their mud nests are kind of ugly, too, and make things awkward when you need to repaint buildings.

I’m not quite sure why they specialize in spiders, it seems like it would be safer to go after things like caterpillars. The only reason I can think of, is that spiders are much less likely to have chemical defenses and toxins than caterpillars do[3]. It may also be that spiders are easier to paralyze for some reason, maybe it’s easier to hit their master nerve ganglion.


[1] Most solitary wasps are pretty mellow that way, because there’s no percentage for them in stinging you unless you are actually killing them. See, if you have a whole nest of social wasps, then it is worth their while to sent a few out to discourage large mammals like us, because even if the defenders get swatted and killed, they are still likely to save the nest from being molested. The survivors can then continue taking care of the grubs, and the colony goes on. A solitary wasp doesn’t have that luxury, though. If she stings you to try to drive you away from the nest, and gets herself killed, then there’s nobody to stock the nest and the whole thing is a loss. It’s actually better for her to abandon a threatened nest and save herself, than to try to defend it. But, if you grab the wasp and try to kill her, she no longer has anything to lose, and that’s when she’ll sting you.

[2] My grandmother had these wind chimes that had kind of lost their chime, they just went “clunk, clunk” when the wind blew instead of ringing. I noticed that the weren’t working, looked into the tubes, and found that I couldn’t actually see through them. So, I took a piece of wire and rammed it through – and found out that the tubes were packed with mud. It seems they were just the right diameter to appeal to the mud daubers, and they’d used them for nests.

[3] Although, there’s one thing about spiders that live next to rivers and lakes. If the spider mainly eats insects that have aquatic larvae, those larvae are likely to have accumulated mercury from the water – particularly if they were predatory larvae preying on other, smaller animals. So, spiders in those conditions can have a very heavy mercury load[4]. This is evidently a problem for birds that eat spiders, because then they have an even larger mercury load, to the point where it can kill them.

[4] What happens with mercury is this: you start with a very tiny quantity in the atmosphere, that eventually gets caught in the rain and carried into rivers and lakes. The mercury then converts to a form that living things will take up. Plants grow, and some of this mercury gets into their tissues. An animal then eats the plants, and the mercury gets into their fat, which holds onto it. So, they end up retaining pretty much all the mercury that they eat, concentrating it to a higher level than it was at in the plants. Then something else eats the first animal, and concentrates the mercury still more. So, if you have a chain that goes something like algae => water flea => carnivorous caddisfly => bluegill => bass => you, there are four stages of mercury concentration before you get it. If we assume that each stage of concentration increases the mercury levels by a factor of ten, then you are looking at 10x10x10x10 = 10,000 times more mercury than if you had just eaten the algae. If, on the other hand, you have algae => carp => you, there’s only one stage of concentration, so you only get 10 times more mercury than the algae, which is much better. Basically, if you want to minimize mercury in your diet, you want to eat terrestrial plants, or animals that eat terrestrial plants, and you really want to avoid eating meat from carnivores that eat other carnivores that eat aquatic animals that eat aquatic plants. Eating meat from bears that have been eating salmon that have been eating other fish would be exactly the wrong thing to do.

[5] Which brings up one of my favorite entries in the Bulwer-Lytton Fiction Contest:

“Terry the Tarantula and Wendy the Wasp were frolicking and cavorting together in the Flowery Meadow, (as they were the best of friends in all the Enchanted Forest of Miggly-Wompsly) when, all of a sudden, and with no warning whatsoever, Wendy accidentally stabbed Terry with her stinger, making her very sad for she knew that soon her poison would paralyze her friend and after a while her eggs would hatch inside him, and then her happy wriggling larva would slowly eat him alive, but Terry tried to smile and would have told her not to be sad as this was how the Circle of Life was continued, but he was in too much pain and, as I mentioned before, paralyzed.”

(Delano Lopez, Washington, DC, in the “Children’s Story” category, 2001)

119 Responses
  1. Mark Havnes permalink
    July 3, 2017

    I just saw a blue mud dauber wasp buzzing around, low to the ground, in bright morning sunshine. It is one of the most beautiful creatures I have ever witnessed. A deep dark purplish iridescence that that left me breathless

  2. Susan Perz permalink
    July 14, 2017

    Hi. So I have a couple wasps nests on my back porch of blue mud daybeds. They are beautiful and they have built tubes under my porch which thanks to you I now know what they are. They fly around a lot and I am allergic to stings. I would like to enjoy my porch but they are so beautiful I hate to kill them. Is it possible to safely coexist with them under these circumstances since they are not aggressive? It makes me very nervous so I would really appreciate suggestions. Are they rare or endangered. I have also found several paralyzed spiders in spider webs which I found confusing until I read your article. I don’t like spiders so it’s good that they eat them. I am on several acres with a very large creek in my backyard and a swimming pool that is now a pond until I can afford to fix it which will hopefully be this year.

  3. Wendy permalink
    July 14, 2017

    Susan when I had a bunch hatch in my house (the plants had been outside) I was worried about getting stung too but they were very peaceful. They would even walk out the front door or wait for the window to be opened. Even accidently touched one that was hiding in my purse. If would think that if you left them alone they shouldn’t bother you at all.

  4. Crystal H. Rogers permalink
    July 29, 2017

    From Alabama. Every morning,early, when I open my mailbox, a swarm of what appears to be small dirt daubers (Do not think they are dirt daubers) fly out. They have never stung me and do not seem to be interested in me at all , except to get away. They are under the box and opening the lid disturbs them. They are not there at other times of the day. I can see no nest or anything they may have done there, except sleep.
    They are about 3/4 inch long and blue-black. I have dirt daubers, but they are larger than these. They do have 2 sets of wings.
    Do you have any idea what these insects are. Thanks.

  5. July 31, 2017

    Crystal: They may be male mud dauber wasps. The males have a tendency to roost together in “congregations” overnight, and then fly off during the day to look for females to mate with. Male wasps have no stingers, so they are completely harmless, and they clearly aren’t going to be doing any nest building.

  6. Crystal H. Rogers permalink
    July 31, 2017

    Thanks for this info about male mud daubers. This makes a lot of sense. Thanks for your reply.

  7. Stephanie permalink
    June 28, 2018

    I have a bunch of what I think are Blue Mud Daubers hanging out on my wreath on my front door. How do I know if they are nesting? I don’t want to kill them but I don’t want them nesting there either.

  8. June 29, 2018

    Stephanie: If they are nesting females, then there will be some sort of holes that they will be going in and out of – either mud nests from previous wasps, or small-diameter tubes of some sort. This will be pretty noticeable, and I don’t think that a wreath will provide a lot of good sites for them.

    I think it is more likely that you have a congregation of the male mud daubers. The males tend to hang out in groups like that, but the don’t have stingers and don’t build nests. The females are elsewhere.

  9. Stephanie permalink
    June 29, 2018

    Thanks for the info Tim, we just moved to this house in May so I suppose it’s possible there is an old nest somewhere that we wouldn’t be aware of. The house is mostly brick, would they nest in a hole or crack in the brickwork if they could find one? I will have to have a closer look around that area. I’m hoping it’s just the males hanging out. I’m also hoping I’ve identified them correctly. I’m pretty sure I have. We live in Southwestern Ontario and that seems to be the most common wasp in this area that looks like that.

  10. June 29, 2018

    Stephanie: They like either recycled mud nests (which look like blobs of mud stuck to the wall), and holes that are about the diameter of a pencil. Holes in brickwork will do if they are the right diameter, as will the tubes of a lot of common wind chimes. If you don’t see anything like that around your door, then I think it is safe to assume that they are the males.

    You most likely have the ID correct, these are very common wasps. There are a few other species of dark metallic blue-black wasps, but as far as I know they all have nesting habits broadly similar to the Blue Mud Dauber.

  11. Stephanie permalink
    June 29, 2018

    Thanks again for the information

  12. Robin permalink
    July 16, 2018

    I live in an apartment complex in Oregon. We have what I think are blue mud dabbers. But I’ve read that they are not aggressive. These however are buzzing around my back porch & when I try to go outside they swarm me. One flew at my face & tried to go up my nose. They have chased the kids & being kids seeing such a big “bee” they scream, run, & some of them got stung. I don’t want to hurt them if they eat spiders but can’t have them hurt the kids… Any suggestions.

  13. July 16, 2018

    Robin: That does not sound at all like mud daubers, they are solitary wasps that don’t occur in that kind of numbers. What you have sounds more like some variety of social wasp, some of which are pretty dark in color. If they are really big wasps, bigger than a honeybee, and mostly dark with only a few white stripes, then I think it is much more likely that they are Bald-Faced Hornets. These are foul-tempered and inclined to attack anytime you approach their nest, and the sting is very painful. If there is a nest that looks like a big ball of paper, then that’s them. There are some other, smaller black wasps that are also possibilities, that nest in crevices and holes without a visible nest.

  14. s osborne permalink
    July 17, 2018

    we have been stung several times my dog was stung a couple of times. we cannot find the nest do you have any sugge3tion

  15. July 18, 2018

    s osborne:

    If you can’t find the nest, the only thing I can suggest is to mark the area where they are aggressive and avoid it, and maybe build or buy a wasp trap to reduce their numbers.

  16. Tondy in WA permalink
    April 12, 2019

    I am interested in attracting a few more blue mud daubers to my property. Could I simulate abandoned tubes with paper straws maybe?
    I Have seen them here, they were completely docile. one got in the house, picked it up and put it back outside. If I make an attempt to build them a home, do the tubes go vertically or horizontally like a mason bee? I can find a protected eve on any side of my house or shed for them, which side would they prefer? East with morning sun? or North cool and shady all the time? Any advice would be appreciated, I could always give it a shot with one on each wall and see which if any become occupied.

  17. Crystal Rogers permalink
    August 15, 2019

    Back again from 2017. Blue daubers (male, as per your suggestion) have continued to roost under my mail box. Suddenly, they are gone, starting the first week of August. What happened to them? I have also noticed not as many nests as in past years. Can you provide more info or suggestions of where to find info on what may be happening?

  18. Shellie Ke permalink
    August 30, 2019

    So could blue mud daubers be using carpenter bee holes? If so, are they causing damage? Are they keeping the carpenter bees away (hopefully!)?

  19. Crystal Rogers permalink
    August 31, 2019

    No, these guys sleep under the lid of my mailbox and there are no holes or other evidence of nests. These have nothing to do with carpenter bees, which I have plenty of also.

Comments are closed.