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Photo#268094
Spider ID Request - Cybaeus - female

Spider ID Request - Cybaeus - Female
Herring Run Watershed, Baltimore City County, Maryland, USA
April 21, 2009
Observed under a rock in the relatively intact oak woodland inside my local cemetery.

Images of this individual: tag all
Spider ID Request - Cybaeus - female Spider ID Request - Cybaeus - female

I've been keeping...
a very similar looking spider:

She has since grown into what appears to be an Amaurobious ferox:

With permission from the others I think this one might be better placed in Amaurobiidae.

 
Tough one
We also have very similar spiders in Cybaeus. Compare the spider above to C. shoshoneus.

From Robb Bennett:
Hello Thomas -- many thanks for your enquiry, I'm always happy to reply to such questions.

Cybaeus is a very interesting genus with huge species diversity in woodlands of western North America (particularly CA and southern OR) and in Japan. One interesting aspect of the genus is that very few species occur in woodlands of eastern North America -- there are only 3: C. giganteus Banks, C. patritus Bishop & Crosby, and C. silicis Barrows. Of these, C. patritus is restricted to the southern Appalachians in TN and NC. The other two species are more widespread and, although I only know of Maryland records for C. silicis, both silicis and giganteus are likely to occur in Maryland. Cybaeus giganteus ranges from NY to GA & AB, C. silicis ranges from OH and MD to NC -- both species are relatively common.

Regarding identification -- the short story is that I THINK your specimen is a female of Cybaeus silicis. Females of the 3 eastern NA species are very difficult to tell apart. You can rule out patritus on basis of distribution; separating silicis from giganteus is primarily a value judgement based primarily on size and somewhat on leg banding:
carapace (top of the "head" end of the spider, the part with legs attached (sorry if you know this!!) length in C giganteus females that I have looked at ranges from 4.5 to 5.4 mm (a relatively large spider), in C. silicis females the carapace length range is 3.4 to 4.0 mm (not really a lot different from giganteus!).
Additionally, C. silicis legs are usually at least faintly banded while those of C. giganteus usually show no evidence of banding. As Rod Crawford noted, you can see banding on at least one leg in the BugGuide image (back right).
Based on the leg banding my tentative ID would be female Cybaeus silicis. If there was a good indication of scale in the image, this would provide stronger indication of ID. If you collected the specimen and can figure out an easy way to measure the carapace, then your opinion on ID will be as good as mine! (I measured dead museum specimens under a dissecting microscope -- I realize that most folks don't have access to such equipment and would rather not have to kill specimens just in order to identify them.

The BEST way to get positive ID of your Cybaeus is to try to find mature males -- these are usually only found later in the summer and through the fall until the weather turns (you can usually find females year-round). Males are much easier to identify than are females and males of the 3 eastern NA species are quite easy to tell apart, even from digital images as long as you have a clear shot of the male pedipalp (the "feelers" -- again, sorry if you know what a pedipalp is!). You can usually ID a mature male using a good hand lens although using a dissecting microscope is the best way.


Enjoy!

Robb
Robb Bennett, PhD
Editor-in-Chief / Directeur scientifique en chef
The Canadian Entomologist

From Rod Crawford:
"Does look like an amaurobiid at first glance, but based on the
carapace and leg banding, I'm guessing Cybaeus sp., Cybaeidae."

 
-
Thanks, Rod (and Lynnette). See above comment from Robb Bennett.

 
Looks good,
Now you just have to go out and find a male!

 
From Robb Bennett about that:
RE Cybaeus males -- they generally roam about at night, looking for receptive females, and hide-out during the day. The females of course, generally stay put. So, males are not quite so likely to be found in association with a particular web under a particular rock as are females. And, if a male finds a receptive female, they don't hang around all that long so finding a male with the female in your image would be quite lucky for you. Therefore, it is quite likely that you will find male(s) in the same vicinity but you may have to turn over a bunch of rocks before you find a specimen. Other good spots to look will be under any sort of chunks of wood or other stuff in the neighbouring woodland; actually, just about any pile of "stuff" (including human junk) in the woods or nearby is likely to harbour specimens during the day. I live in a wooded area on southern Vancouver Island and regularly find at least two species of Cybaeus in the firewood pile outside my house. If you get into "serious" collecting and start using pitfall traps -- these are an excellent way to capture wandering male spiders of many types, including Cybaeus.

Try the Hacklemesh Weavers
in the Amaurobiidae

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