Pupae of braconid wasps. Arroyo Chico, Tucson, Pima County, Arizona, USA. 18 October 2008.
I found lots of these in a thicket of climbing milkweed (Funastrum cynanchoides) that was frequented by queen butterflies (Danaus gilippus) earlier in the year. I suspect that these wasps emerged from queen caterpillars.
If you think this observation is inaccurate, please add an ID, participate in the quality assessment above, or describe the inaccuracy in a comment.