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Sexing a Black & Yellow Mud Dauber Wasp - Sceliphron caementarium - female

Sexing a Black & Yellow Mud Dauber Wasp - Sceliphron caementarium - Female
Tonopah Desert, Maricopa County, Arizona, USA
April 14, 2015
Size: 33mm
These are images of a female Thread-waisted Wasp called a Black and Yellow Mud Dauber, Sceliphron caementarium. I noticed that many of the images of this species on the BugGuige are not sexed and that most of them appear to be females.
Here is a link to this wasp's short video: (3.5min. duration) ♀ Black & Yellow Mud Dauber - Sceliphron caementarium

Any images involving burrow interactions, mud-building construction or predation are probably going to be female wasps. From the clearer images of the mating pairs or even the threesome-sexual interactions, you can see a bit of the dimorphism of this species. Petiole colors and overall wasp sizes are always somewhat variable between locations and also in any one location.

Here are three ways to sex these wasps and there may be more methods. This requires clear images of the abdominal area. All numbers are approximations, based on my limited skills. By default, the female wasps will generally have larger abdomens, but they can also be larger wasps in overall size, which may add to some confusion. The dimorphic differences are subtle and very hard to determine, without accurate measurements or direct comparisons.
1) - average abdomen length (male's = 0.65 to 0.85 times the length of female's)
2a) - abdomen (A) to petiole (B) length ratio (A/B) - (male = 0.6 to 1.3, female = 1.5 to 1.9)
2b) - In the case of the wasp pictured above, this ratio is approximately: A/B = 1.78
3) - abdominal segment number and segment width (lateral or dorsal view) - (male = 7 short tergites, female = 6 long tergites)

Images of this individual: tag all
Sexing a Black & Yellow Mud Dauber Wasp - Sceliphron caementarium - female Sexing a Black & Yellow Mud Dauber Wasp - Sceliphron caementarium - female Sexing a Black & Yellow Mud Dauber Wasp - Sceliphron caementarium - female Sexing a Black & Yellow Mud Dauber Wasp - Sceliphron caementarium - female Sexing a Black & Yellow Mud Dauber Wasp - Sceliphron caementarium - female Sexing a Black & Yellow Mud Dauber Wasp - Sceliphron caementarium - female

Note also shape
Female abdomen ends in a gradually tapering point whereas male is a bit curled and not so pointed. Subtle and hard to quantify but with experience the shape difference is useful even when segments cannot be counted.

John, thanks for placing all of these cool wasps! Yes, I noticed that the ends of the abdomens have more of a difference and also; the male's segments are often hard to count there, because they are so short. They almost blend together and easily get shaded and the female's segments are much easier to count. OK, I'm glad that you agreed with me on the other males images too, wow!

Moved from ID Request.

Candidates for the "Info" tab
Here are the two best mating images:
These are probably male wasps:

Updates to Info page?
Hi Bob. I was thinking of at least updating the Info page by adding a link to this post and all these great tips and photos on sexing. However, I just noticed that you have recently become an editor (congratulations!) and wondered if you'd prefer to actually update the Info page yourself rather than just have me provide a link? I'm happy to do my small part, but know that you would do a more instructive and comprehensive job of it. :)

Feel free to link my images anytime that you think it would be helpful.
These types of images are "unmarked-as-representative" and will not be seen in the browser: Also, they will not show up on the info page, unless posted there with a thumbnail link.

Thanks, Bob - great info !!
Thanks, Bob - great info !!

For what it is worth there an interesting
thing pointed out to me by Richard Vernier on one of my uploads. He said that the petiole tends to be yellow in the west, and black in the east. That seems important, and for all of the west coast versus east coast individuals this seemed to hold true. I seem to remember that I heard that the petiole is black in Europe as well. I'll link to the original comment. It may possibly be worth putting on the species info page.

The original post was twelve years ago, but to me that makes it all the more interesting and worth noting.

I know there is a place it the forum to suggest this kind of addition to species pages, but I am not sure if I want to. I feel I am among friends here, so I just mention it here for now.

For the most part, that is generally true. ( AZ & CA) However, surfing the data tab will show that there are several exceptions out there. (black in WA, yellow in NB & TX)
Sometimes there are odd-balls too: ♂ Did you watch her ID video? It's one of my favorites.

ID video
Bob, can you provide the link to the ID video you mention here?

It's in the text under her image. (above) All you have to do is click on it, lol.

I got it now, thank you! They don't call me slow for nothing!
That's a great video with great views, and I love seeing the wasp go free at the end. :)

That video was a real eye opener, Bob!
I have been a little troubled by my reluctance to end the life of an insect in order to better examine it. For one thing, two dimensional views do not really give you a feel for how all the structures work together. This video was excellent! Seeing the insect from above, below, Side, front, and behind while in motion was great! I have to admit I have never cared much for making videos. I think a big part of that is because of the computer and software resources needed. I used to put clips together using NERO 6. It was really simple to use, but is not compatible with windows 10.

The reason I am troubled by the lack of acknowledgement of the yellow petioles on the west coast is that the descriptions on Wikipedia, and iNaturalist both describe S. caementarium as "having a black petiole", which is very misleading. If an interested party were trying to identify a wasp and came up with those two sources stating that the petiole must be black, and then they looked on Bugguide and did not see anything that specifically said that in the west the petiole is very likely to be yellow, then they would likely conclude that their yellow specimen must be some other species of wasp.

What is sort of cool is that they have a very high resolution photo on Wikipedia of a specimen, I believe it is from Europe, that not only has a black petiole, but the bases of the antennas are distinctly orange! I realize that color differences may not be important, however, one supposes that descriptions should mention striking differences, and trends like these.

Lastly, and this is not definite, but I thought that S. caementarium was considered an invasive species in Europe. Now this is complete speculation, but I am so used to seeing invasive hymenoptera like the European paper wasp, and the Wool Carder Bee to name a couple that have come from Europe and ended up here. It makes me wonder if the ones that became established in Europe came the US east coast. Just food for thought.

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