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Photo#105599
Predacious Diving Beetle? - Colymbetes longulus

Predacious Diving Beetle? - Colymbetes longulus
Bethlehem, Grafton County, New Hampshire, USA
April 24, 2007
Size: ~20mm

Images of this individual: tag all
Predacious Diving Beetle? - Colymbetes longulus Predacious Diving Beetle? - Colymbetes longulus Predacious Diving Beetle? - Colymbetes longulus Predacious Diving Beetle? - Colymbetes longulus Predacious Diving Beetle - Colymbetes longulus Predacious Diving Beetle? - Colymbetes longulus

added close-up of striations
Does this new picture clear up the identification? The size of ~20mm is an estimate, and it could be 16-18mm.
Most times I upload the pictures larger than the 560 X 560 format, but only editors can open the larger pics. Maybe you can ask to become an editor. That also allows you to create new pages in the guide.

 
Wow, this new picture really
Wow, this new picture really help to confirm the genus Colymbetes. Now if you can affirm that the ventral surface + the legs are totally black like it appear on the underside picture, the species C. paykulli will be confirmed.

 
2nd Wow,
I agree with Pierre-Marc: confirmed Colymbetes. It's often difficult to capture subtle details like these groves and the dim color variations like the lateral pale areas (flash washed them out). You might think about adding the closeup of the groves to ID section on the genus page. Great addition to the Guide.

 
ventral close-up added
The underside is entirely jet black, and the legs are black with reddish spines.

Moved
I couldn't find any pictures of Neoscutopterus, but one of a Rhan*tus that looked like this, and it said that the Neoscutopterus can be confused with it, but are over 13mm.

 
Neoscutopterus sp.
If you go back to the web site here that I'm guessing you're referencing from a google search, and search on "Neoscutopterus", you'll actually find photos of both species listed for our area. (why they don't appear in a google search is beyond me?)

Downie and Arnett key N. augustus as "pronotum with lateral margins markedly deflexted downward near hind angle", and N. hornii as "lateral margins more or less straight or evenly and gradually arcuate in side view". But in the species descriptions it mentions that N. hornii as "elytra with puctures deeply impressed to apex", and N. augustus as "puntures distinctly marked basally, obsolete apically". From what I can see of yours, the punctures seem to fit N. augustus better. But as you can probably enlarge your shots, suggest you decide this one (if possible). The MCZ type photo is found here

Both species are listed at 16mm, although I've found sizes in Downie and Arnett are not always accurate.

Either way, it's another new species for BugGuide :)

 
transverse groves?
wait just a minute! after re-looking at your "water" shot and seeing a lot more pale edge to the elytra and possibly also the pronotum, and possibly 2 faint pale spots between the eyes, this may not be Neoscutopterus at all but rather Colymbetes. The Colymbetes would have to have "transverse striae" or lots of closely spaced groves across the elytra, which I think I'm seeing in your side shot. If the groves are really there, than from Downie and Arnett this would seem to be C. longulus LeConte (type seen here), and apparently now named C. paykulli Erichson (a google image here that looks like yours). C. longulus size listed as 17-18mm.

Bottom line: If the transverse groves are there on the eyltra, I'd say move it to Colymbetes

 
Yes, you are right
I didn't noticed this groove on the elytra. So Colymbetes sp. is for sure a best identification. And judging on the key of Larson (Predaceous Diving Beetles of the Neartic Region), it can only be the species you mentionned C. paykulli. Only two species have the ventrale surface totally black, and the other one is only known from Western Canada. The size gived in this book is 15.7 to 18.6, so really near to 20mm. I think you can move it to this species with a minimum of misidentification chance.

Neoscutopterus ?
I'm really nor sure, be it could be a Neoscutopterus sp..

Moved
Moved from Beetles.

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