A female Widow Skimmer dragonfly at Prettyboy Reservoir, Baltimore County, Maryland, USA. © 2017 S. D. Stewart

Note: While I initially thought this was a female, widow skimmers are sexually dimorphic, meaning that even though the mature males and females look different, the immature males look similar to the females (this is also not uncommon in birds). A good way to separate the sexes is by their terminal appendages, as nicely illustrated in this post by Walter Sanford. The female has two, while the male has three. In order to determine this, one needs a clear close-up view. Unfortunately the resolution of my images is not quite high enough to determine the sex for certain. When I have the image magnified, it looks to me like there is possibly an epiproct present, but because of the angle of the shot I can’t be sure.

UPDATE: Walter Sanford stopped by and identified it as a female (see comments). Thanks, Walter!