These are images of a male Thread-waisted Wasp called a Blue Mud Wasp
, Chalybion californicum
. Many of the BugGuide images are not sexed and most of them appear to be females.
NOTE: Some of this dimorphism information is also applicable to the sister taxon, Chalybion zimmermanni
Here is a link to his video: (4min. duration) ♂ Blue Mud Wasp - Chalybion californicum
Full Size Image: Click Here
Any images involving burrow interactions, construction or predation are probably going to be female wasps. The females will often rehab the old, abandoned mud-burrows of another wasp, like those of Sceliphron caementarium
. The preferred pray of the female wasps are spiders, like Black Widows. The females are normally solitary, but the males will congregate together at night and sleep in large groups, very close to each other. (touching)
Here are five ways to sex these wasps and there may be more methods. This requires clear images of the abdominal area or the mandibles. Overall abdominal size is approximately the same and the abdomen to petiole ratios are also about the same for both sexes. The dimorphic differences are subtle and very hard to determine, without accurate measurements or direct comparisons.
1) - abdominal tip or apex shape - male = blunt, female = pointed
2a) - two abdominal spurs (length = approx. 0.35mm) - male = 0.50mm from apex, angled laterally about 40deg. from center-line, projecting from underneath last tergite
2b) - two abdominal spurs (length = approx. 0.15mm) - female = directly adjacent to apex, pointed almost parallel to center-line, contacts the base of extended stinger or ovipositor
3a) - abdominal segment number - male = 7 tergites & sternites, female = 6 tergites & sternites
3b) - Sternite edges might also have different shapes. (requires a good ventral view) On the males, the edges are straight and some of the images of female wasps show that they have curved edges on some of the sternites.
4) - mandible shape (ventral view only) - male = sharp edged tips, female = blunt or rounded edges
5) - antenna segments or flagellomeres - male = 11, female = 10