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Photo#218839
Mayfly - Isonychia

Mayfly - Isonychia
Moccasin Lake, Winston, Douglas County, Georgia, USA
August 25, 2008
Size: about 18 mm
Small Mayfly unknown ID, any help would be appreciated.

Slate Drake
This is a female Isonychia subimago. (Although the eyes of Isonychia females are rather large, the eyes of males are even larger--as in the male imago here.)

You have a wealth of Isonychia species in Georgia (8). In fact, one is even named for your state: Isonychia georgiae.

Very nice
Can't help with I.D. but maybe its a subimago? Never seen a black mayfly before though. I can tell you its male.

 
Thank you both
Thanks to both of you for your comments, but I must ask, which is it male or female? There are a lot of Mayflies out now and several different ones. I'll try posting them in the next few days.

 
It is female.
The eye size difference that I mentioned (larger in males, smaller in females) is one of the most obvious ways to determine the gender of most mayflies in the subimago stage. Although there are a few exceptions (Anthopotamus, Caenis, and Tricorythodes for example), the comparative difference between male and female eyes should become obvious as you scan through many of the mayfly photos in the Guide. If you click on the link that I provided in my previous post, you can see the comparative difference in Isonychia.

Once the molt from subimago to imago is accomplished, additional differences between male and female can be seen. The males develop elongated forelegs (for grasping the females during aerial mating) and the male terminalia (especially the forceps or "claspers") can be seen at the tip of the abdomen. (Male terminalia can sometimes be seen in the subimago stage, but it is usually more obvious in photos of imagoes.)

In the field, you will also notice that female mayflies are usually larger than males and that some genera/species display differences in coloration/markings between male and female, especially in the imago stage.

I look forward to seeing more of your mayfly photos.

Best,
Lloyd

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