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Photo#1092574
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.

 
Thanks!
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! Did you find any obvious errors in my math? Can you update the "Info" tab or do we need to contact someone about doing that?

Moved
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. :)

 
OK
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 !!