What's That Bug? does not endorse extermination

Subject: Unidentified, Unusual Egg Case
Location: Southern Michigan
April 27, 2013 7:39 pm
Dear Bugman:
I found this unusual looking egg case, while hunting for fossils. It was in a crumbly, sedimentary boulder, along with dozens of sow bugs, which were exposed when I split the rock open. The eggs are visible as round bumps through the papery/silky covering. Was wondering if some type of spider made this, or another kind of arthropod such as the sow bugs?
Signature: Chris O

What's That with the Sow Bugs???

What’s That with the Sow Bugs???  A Spider Egg Case.

Dear Chris,
We do not recognize this thing, but we would not rule out a fungus.  We are posting this as unidentified and we hope that either we or our readership might find and answer for you.

Dear Daniel:  After looking all over the internet for similar photos & an answer, I found a link on Bug Guide which has an almost identical photo of this type of egg sac.  It appears to be the creation of a type of ground spider.  Species mentioned during my searching are gnaphosid, zelotes and corrinidae.  Here’s a link to the pic on Bug Guide:  http://bugguide.net/node/view/181688/bgpage

Dear Chris,
Thanks so much for following up on this posting.

What's That Bug? does not endorse extermination
Location: Michigan

3 Responses to Spider Egg Case

  1. sure looks like a spider egg sac, according to Track and Sign of Insect by Charley Eiseman.

  2. Suzanne Allan says:


    I received in the mail a book that I had purchased. Inside was an egg case like this one and a black spider with a white circle around his bottom. It looked as though he had no hair on him and the slightest bit of white on his joints on his legs.

  3. Suzanne Allan says:

    Plus… The package came from NJ and the egg sack/spider are attached to cardboard.

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