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Photo#806246
Allegheny or Illinois River Cruiser?? (DDF863) - Macromia illinoiensis

Allegheny or Illinois River Cruiser?? (DDF863) - Macromia illinoiensis
Great Falls NP, Fairfax County, Virginia, USA
July 11, 2010
Have a hard time distinguishing these two. Appreciate any help with ID.

Moved
Moved from ID Request.

Swift (Illinois)
This is illinoiensis. Male M. alleghaniensis has a complete yellow ring around S7, and a nearly complete band around S2, broken dorsally only (but very rarely complete). In the hand, the mesotibial keel of the male is about 20% of the length of the tibia on Allegheny, while it is 25-50% on Swift. These differences do not apply to females.

 
Thanks
Thanks very much. Appears I've misidentified several other cruisers.

 
Macromia
That area should have both Swift (Illinois form) and Allegheny River Cruisers present, so keep looking! Check out this page on MD cruiser identification by Dave Czaplak.

http://www.odolep.com/d_macromiinae/macromia_id.htm

 
Request
Could you check photo I just added to an earlier request - closeup of abdomen and S7 - Photo#806315
Per your comments and looking at the other photos, I believe the previous photo is also an Illinois.

Thanks.

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