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For Insects, Spiders & Their Kin
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Carabid - Tachys

Carabid - Tachys
Houston, Harris County, Texas, USA
September 2, 2007
Size: 1.5 mm
At a light.

Moved from Trechinae.

Moved from Ground Beetles.

one of the genera around Tachys.

"Pericompsus ephippiatus" one of many possible
This bembidiine looks very similar to the Pericompsus ephippiatus posted by Tim R. Moyer this month. Most importantly, the image suggests ("wishfully") the characteristic six well-impressed striae per elytron which are much reduced laterally in similar genera. P. ephippiatus known in TX is allopatric with P. laetulus restricted to AZ and NM. However, if measurement 1.5 mm is indeed accurate, then my suggestion is wrong as P. ephippiatus should be 2.5-3.2 mm. Only Polyderis (but with vanished striae) gets this small and there are 3 species in TX. Finally, if the lateral elytral striae do indeed vanish laterally, then Paratachys should be considered --- further supported by the hint of elytral iridescence. All these speculations mean that I would need to scope the specimen for a secure identification.

Thank you
for the help. I did measure it and 1.5 millimeters is correct. I'm glad we have you and Boris on Bugguide!

Close to Paratachys
in habitus, coloration, shininess, and suggestion of elytral iridescence. Image reminds me of P. scitulus in my area, also known in TX. Unfortunately body length "1.5 mm" is very tiny --- way too small for any Paratachys that I'm aware of. In TX there are at least 9 species of Paratachys but almost all are > 2mm. In TX only two carabid species are 1.5mm and these belong to genus Polyderis - the smallest carabids in North America! Of the two, Polyderis rufotestacea comes closest as it is uniformly rufo-testaceous and does have elytra with 3-4 evident striae. But Polyderis should be duller, not so shiny as in image. In the end, I am unable to decide on genus Paratachys vs Polyderis given the "1.5mm" and this image with rather limited detail.

Maybe it was
somewhere between 1.5 and 2 mm. It was not 2.5 to 3. I really did measure it!

Thanks for all the help.

Poylyderis rufotestacea
is now the species that I favor for this Bembidiine based on size under 2 mm, rather uniformly pale red-yellow color, sinuate pronotum with sharp hind angles, 3 to 4 distinct elytral striae, and TX location. Recently I examined several specimens of this species collected in adjacent AR which look very similar to this image. However, there should not be dark cloud in middle of elytra as possibly suggested by this image -- hopefully just an optical illusion. Otherwise the rest fits.

should I move it Tachys? Thanks for the ID!