Black Widow
@NYAN If she found it in Arizona, it's likely L. hesperus, but if she got it from somewhere else, it might be L. mactans.
 
@NYAN I've seen a lot of reference to hourglass shape as a diagnostic feature, but in the description on BugGuide for every North American species it notes high variability in the hourglass (including partially and completely missing). Is there another resource that clarifies whether the hourglass shape is diagnostic or not?
 
@dangerforceidle There is sometimes variability, however when there is you can still distinguish usually. It’s mostly a skill that I’ve acquired looking at widows so many times. I’ve found that hesperus will generally have a mostly symmetric hourglass, or sometimes a broken one, like variolus. Variolus is easy, as is mactans usually. Geometricus will have a larger bottom part and there isn’t much variability.
 
@NYAN @Ungoliant, I understand, yes. But with variability of the hourglass comes uncertainty -- it means the hourglass is not truly diagnostic except for tendencies and 'best guess.' L. mactans can have a broken hourglass, for example, and overlaps pretty strongly in range with L. variolus. How can you be certain with such variability?
 
@dangerforceidle

I have yet to see a mactans with a broken hourglass. You can still sometimes see the general characteristics even with a unique hourglass also. It’s a bit hard to explain but I have a bit of an eye for identifying the different species.
 

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