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Photo#1603916
Clamp-tipped emerald exuvia - Somatochlora tenebrosa

Clamp-tipped emerald exuvia - Somatochlora tenebrosa
Walpole, Norfolk County, Massachusetts, USA
August 8, 2018
Size: 13.1 mm
Inside culvert connecting to Pettee's Pond. Larger image.

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Clamp-tipped emerald exuvia - Somatochlora tenebrosa Clamp-tipped emerald exuvia - Somatochlora tenebrosa Clamp-tipped emerald exuvia - Somatochlora tenebrosa Clamp-tipped emerald exuvia - Somatochlora tenebrosa

species ID
This and two other exuvia found nearby, as well as a fourth from Pope's Pond in Milton, were from typical small (< 5 acres) muddy-bottomed suburban impoundments rather than the small streams usually cited for S. tenebrosa. In addition, the three I measured were all 13-14 mm rather than ~20 mm cited in published sources. However, of the four non-state-listed congeners recorded in MA, (S. minor, S. tenebrosa, S. williamsoni, and S. walshii), I concluded the following based on the drawings on P. 410 Of Needham, Westfall, and May, 2014:

--not S. minor because S. minor lacks fringe of short setae on rear dorsal edge of 8th and 9th tergites
--not S. walshii because dorsal spine on 8th tergite extends over about 1/3 length of 9th tergite, not half or more
--not S. williamsoni because dorsal spine on 9th tergite extends nearly all the way over 10th tergite, not about 1/4 its length

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