The other day a slightly odd forktail caught my eye. It resembled a male Eastern Forktail (Ischnura verticalis) with a bright green thorax and mostly black abdomen, but the tip of the abdomen had a very reduced blue pattern different from any species of forktail that I could recall. Netting it, I was surprised to see it was a female. I put it in an envelope to examine later.
At home I gave it a close look. It had a vulvar spine  and what I could "read" of the prothorax and mesostigmal plates  under my microscope indicated it was an Eastern Forktail. However,we'd never seen an illustration of one so strongly male-like and the bright blue pattern on the dorsal abdomen tip was unlike any we'd seen -- on any forktail.
Many species of damselfly have a female morph that is colored like a male. They are not only the minority morph in populations, but also very rarely seen. First, once they get older and more pruinose, they look just like typical females. And of course, not too many people look at enough inch-long insanely abundant insects in the grass to pick them out.
I solicited comments on my photos. Both Nick Donnelly and Dennis Paulson confirmed that this was a rare andromorphic female Eastern Forktail (Dennis has seen only one in his long career). In fact, the incidence of andromorphs in this species is under 1%. Here are the photos; all are clickable for larger sizes. More background follows.
As an aside, Russet-tipped Clubtails (Stylurus plagiatus) are increasing in number at the same site. A few very teneral individuals were found, along with a number of older ones, and a pair in tandem. Here's a cooperative male:
The evolution and frequency of female color morphs in Holarctic Odonata: why are male-like females typically the minority? (PDF). Ola M. Fincke, Reinhard Jödicke, Dennis R. Paulson and Thomas D. Schultz. 2005. International Journal of Odonatology: 183-212.
 Vulvar spine = point on the underside of the 8th abdominal segment in some damselflies; Eastern Forktails have one, Fragile Forktails (I. posita, the other common forktail in my area) do not.
 Prothorax and mesostigmal plates = structures behind the head of female Odonata that enable the male claspers to fit and lock on when the pair are in a mating wheel.