Female Drunella grandis (Western Green Drake) Mayfly DunView 6 PicturesI collected this specimen while away from all my good photography equipment except the camera and one of my macro lenses, so I made do. The lighting is from lamps in a hotel room, so it was hard to edit for really true colors, but I tried to get as close as possible. The body was 13 mm long, wing 19 mm long.
Male Epeorus (Little Maryatts) Mayfly DunView 12 PicturesI hoped this dun would molt into a spinner for a positive ID, but it didn't. My best guess is Epeorus dulciana, but that's only because that's the smallest western Epeorus species, and this specimen is smaller than any of the others, with a body length of 5.3 mm (although it would be longer as a spinner) and a wing length of 8.5 mm.
The body and front wing were both about 15.5 mm long, while the cerci (Cercus: The left and right "tails" of an insect are known as the cerci or caudal cerci. The middle tail of a three-tailed insect is not.) were 40 mm long.
Abdomen: The rear and usually the longest (ten-segmented in mayflies) portion of an insect's body, to which the tails are attached.
Cerci: The left and right "tails" of an insect are known as the cerci or caudal cerci. The middle tail of a three-tailed insect is not.
Dun: Mayflies have two adult stages. They first emerge from the water as duns (scientifically known as the subimago stage). They then molt into the spinner (imago) stage, in which they mate and die. Sometimes the word "dun" is confusingly used to refer to a brownish gray color in fly tying materials.
Molt: When aquatic insects with hard exoskeletons (like mayfly and stonefly nymphs) grow bigger, their exoskeleton does not grow with them. Instead they grow a new, larger one underneath and shed the old one when it's too small. This process is called molting.
Spinner: There are two winged stages of adult mayflies. They emerge from the water as duns, molt on land (usually) into their fully mature stage, spinners. As spinners, they mate, lay eggs, and die.