The twelve-spotted skimmer has twelve dark brown wing spots. Males have eight additional spots that are white. Females lack the white spots.
Young males that have recently emerged as adults resemble females, with brown bodies with a yellow stripe along each side of the abdomen. As the males mature, a whitish (pruinose) coating develops on their bodies that can be rubbed off. As the male ages, the white coating may begin to look bluish.
An older name for this dragonfly was the ten-spot skimmer. Apparently, people were counting the middle spots, closest to the body, as a single spot that stretches across from wing to wing, yielding five spots for the front pair of wings and five for the hindwings.
Learn more about this and other dragonflies on their group page.